I found a rogue homebrew subclass i wanted to use in a friends campaign and they said i could, i just don't know how to add it. and before you say yes i have gone on optional feature manager but all it says is:
You currently have no available optional class features for this class. Unlock all official options in the Marketplace or create them for Homebrew Subclasses.
So do i have to create my own? and if i do, what's the point in publishing it?

Okay, few things to clear up:

1. Optional class features don't have anything to do with using a homebrew creation. You want to enable Homebrew Content in the character builder
2. In order to use someone else's homebrew, you need to add it to your collection. You do this by going to the bottom of the homebrew and clicking the Add To My Collection button
3. This button will only appear if you have an active Hero or Master Tier subscription

i have homebrew enabled and i have added to collection and i have hero subscription it's just i don't know how to select the subclass in the character builder. Thanks for trying to help though :)

Is your character the right level to select a subclass? It varies based on class between level 1 and 3

For a rogue, you won’t select a subclass until 3rd level.

I tried changing the level as well. I put my character to 3, then 2, then 3 again, then 20, and nothing changed.

You choose your subclass in the 3rd level feature named “Roguish Archetype:”

In addition, please see the General Homebrew FAQ #5 for additional troubleshooting: (https://www.dndbeyond.com/forums/dungeons-dragons-discussion/homebrew-house-rules/131411-a-homebrewers-how-to-faq).

Thank you so much. Issue is sorted.