i am really new to DMing and i'm trying to figure out how to transition my players from one part of the quest to another. (ie. from defeating the orcs that were terrorizing the village to visiting the capitol city, etc.) but so far i feel like all the transitions i have planned/written are essentially "go speak to [insert npc]" or "you'll have to visit [...] for that" and then the NPC tells them where they need to go, or something along those lines. what are some other types of transitions I could use? thank you so so so much!

First, I’d take a step back and say why force them to go to the Capitol city? 
I like to run games that are more, throw out a bunch of plot hooks, and see which ones the party takes. Then, I keep in mind the hooks they didn’t take. (Ignore the bandits, and they grow stronger. Don’t go save the blacksmith’s daughter, and something happens to her (maybe she dies, maybe she becomes like her kidnappers, maybe she makes a deal with a fiend and becomes a warlock so she has power to escape on her own.) It makes it feel like a living world where choices matter, instead of people standing around with an exclamation mark over their head waiting for the PCs to show up.

To try and answer the question more directly, it’s really good to seed future plot points as you are still developing one story arc. So before they even deal with the bandits, they hear about strange things happening at the capitol city. And there’s always the background card — one of the PCs finds out their brother has joined the death cult in the capitol. (And at the same time, there’s strange rumors of things happening along the coast, since that’s what you have planned for the next arc.)

Think of a campaign like a flow chart. At each event there are several possible outcomes. Each outcome leads down a new path to a new event. That event has several possible outcomes, etc, etc, etc. "How" does one scene lead to another? Two ways - one, you provide certain clues in the aftermath of the scene. And two, the players may say their characters do certain things at the end of the scene. 

So let's use your example. The party has just defeated a band of orcs that has been terrorizing a village. At the end of the battle the party loots the corpses. You can tell them that when they search the leader of the orcs they find a clue that implicates an important political figure from Capitol City. Maybe it's a sack of gold coins and a letter from that person. So now the party may want to investigate why a politician in Capitol City is paying orcs to attack local villages. 

Or maybe the fight ends and the party's ranger wants to look for tracks to see where the orcs came from. So you tell them they find tracks leading up into the hills where they come to a clearing. In the clearing the footprints of the orcs mingle with the hoof prints of several horses. There are no signs of battle here. And the hoof prints lead down a path toward the other side of the village. So clearly some people on horseback from the village met with the orcs to plan the attack on the village.

Or maybe as they're looting the bodies they find one orc who is only mostly dead. Someone in the party tries to interrogate the orc, in Common, and the orc answers the questions - in Common! Why does this orc warrior know the Common tongue? And maybe the orcs says the village attacked them first and the orcs were just seeking revenge. 

So you finished one scene and you now have three potential paths to follow. Now think up two or three possible scenes that might results from each of these three. Then two or three from each of those, etc, etc, etc. You don't actually have to completely flesh out every detail of every one of those potential scenes, since most of them won't happen. Just keep thinking into the future, trying to decipher the probable ramifications of each of the party's decisions. 

Oh! Wait! Maybe when the party is looting the orcs they find a crudely drawn map of the region with several villages marked on it. They manage to decipher that this village is one on the map. So they may want to travel to the next village to warn them that an orc attack may be incoming. 

I agree with the answers you've already been given, but I'm going to give you another angle too.

Read more published adventures/campaigns.

As with many creative endeavours exposure to other people's work fuels, feeds, and helps to develop your own creative works. Read absolutely as many other adventures that you can, because in doing so you'll get an idea of what you think works, what you think doesn't, and it genuinely helps to refine the adventures you create. There's a reason why most TTRPGs contain lists of inspirational reading materials. If you really can't bring yourself to read, then get yourself in as many different one-shot games as possible as a player. See how, and why, and what other GMs do. 

Humble Bundle and the Pathfinder system is great for this. They regularly have bundles of adventures and supplements for a dirt cheap price. I've bought a few of them especially for that reason. I'll read all of the PDFs at least once. You can ignore the system specific stuff (it's rarely relevant) and just look at how the world has been built, how the quests link together. Eventually you will work out what you like and what you don't. I highly recommend looking at the way the Quests work in Dragon of Icespire Peak, Lost Mine of Phandelver, and Dragons of Stormwreck Isle. If you can get hold of it from a library, Extinction Curse (a Pathfinder Adventure Path) is a really good example of an adventure too. If you want to get more in depth and more advanced I'd recommend Curse of Strahd, and Pathfinder's Feast of the Blood Lords. As I say, a good modern library will likely have these to borrow in PDF if not able to request the physical copies (though I'm in the UK). These adventures are all pretty varied and in a weird way similar. There's a good mix of different quest styles and links between them all.

Often you'll find NPCs are involved, but more usually it'll be as a result of the players undertaking an investigation or exploration of a location. Players do need to do their share of the heavy lifting after all. Often an investigation will lead to either a location, a resource (book, tablet, artefact), or an NPC. That's just kinda the nature of the beast.