Hello! I am rather new to D&D, and I wanted to make a character for a campaign that I just joined. 
The concept I came up with for my character is either a warlock, sorcerer, or wizard that has an amulet around their neck that houses a spirit that will serve as rp flavor. He also would be a summoner of creatures through a personal magical deck.
Okay, if it wasn't obvious, I'm making basically a yugioh protag character but in D&D. I'm running into some trouble with figuring out what race, class, and other various factors for him. 
Does anyone have advice on what class, race, and various factors would be good for this?

Thank you for the advice in advance!

If the focus is on the summoning spells, wizard is your best choice of the three you listed, followed by warlock. Wizard also gets you find familiar, as does warlock's Pact of the Chain. Keep in mind a lot of those spells are higher level though, 3rd at least for wizards, so your 'deck' of creatures will be pretty limited in Tier I

You might also want to consider druid, which also gets a bunch of summon/conjure creature spells, and a couple of the subclasses (Shephard and Wildfire) also get you a bonus summoning feature which might be a good fit and give you uses for your Wildshape if you don't ever intend on turning into an animal yourself. Druid also gets summon beast as a 2nd level spell, so you're getting to those summons a bit earlier than wizard or warlock

Race doesn't particularly matter for flavor, although some races might get you languages that would be useful (genasi so you can speak Primordial to any elementals you bring out, or forest gnome to talk to small beasts)

There are also ways you can work in the amulet mechanically (Undead patron for warlock, or something like Divination wizard where the spirit in the amulet is giving you whispers of the future to explain your Portent feature, for instance) but if it's purely just for RP you don't need to worry about it

Aasimar lore includes an angel that guides them. So you can flavour that the angel is the spirit in the amulet, or the amulet is a conduit to them.

There's the Genie Warlock where you can have an amulet that opens, like a locket. The genie being your guide and patron that provides your powers. 

All I got right now, but I'm sure there will be more to come. 

What kind of point buy ability score spreads should I do for my wizard then?

Quote from VyseLupin >>

What kind of point buy ability score spreads should I do for my wizard then?

 if you're going Wizard, you'd want Int Con Dex as your main priority. with Str as least important. Wis and Cha aren't the worst things to have.

Just a suggestion, but I wouldn't necessarily focus too hard on summoning/conjuration spells. Literally every effect can be reflavored as a critter getting called from some otherworldly dimension, doing something and getting pulled back to wherever it came from when it's done. Some spells from other schools already do just that to begin with (Chill Touch for instance creates a "ghostly, skeletal hand" that disappears after a turn) but any fire spell damage can be some variation on a fire elemental getting sent after a target, Hold Person could be animated chains appearing and binding someone, and so on. 

Someone once told me that dex is important for wizards so they can aim their spells, is that correct?
(edit) sorry i just realized i replied to the wrong post

Someone once told me that dex is important for wizards so they can aim their spells, is that correct? Also, would I need cha to get a better handle on my summons?

Quote from VyseLupin >>

Someone once told me that dex is important for wizards so they can aim their spells, is that correct? Also, would I need cha to get a better handle on my summons?

No, DEX is important for AC so you don't take damage as often. It has no effect on aiming spells -- that's based on INT if you're a wizard

All your spellcasting will be based on INT -- CHA doesn't matter for a wizard's summoning spells. It might be a bit helpful if you're summoning something that isn't immediately friendly with you and you need to bargain with to get its help, but that's about it. If you were a different type of spellcaster (warlock or sorcerer), then CHA would be your primary spellcasting stat 

Quote from VyseLupin >>

Someone once told me that dex is important for wizards so they can aim their spells, is that correct? Also, would I need cha to get a better handle on my summons?

 
No, that is not correct.

Dex is used for Armour Class and using ranged weapons. Most wizards don't use ranged weapons - they often use spells instead.

A wizard uses their spellcasting ability, Intelligence, for all spell attacks.

Cha is not needed to handle summons. There's one or two where it can help but for most summons cha is irrelevant as most summons are bound to obey you. You will need to check the text of the spell that provides the summon.