Doom community maps

[TwelvNighn]

I wanted to join a community project,

but I don't know how to. 

so can anyone help me?

[Silhouette 03]

I'd recommend  either the DW maximum project or the DW mega project. They're open to all levels of experience in mapping, and there is plenty of time to submit a map.

[MFG38]

Just find a community project that intrigues you and let the host know you want to join. Provided the slots aren't all taken, that's honestly all it takes.

[DynamiteKaitorn]

Pineapple Under the Sea Speedmapping (PUSS for short) doesn't have limits on how many maps can be made usually, so they're easy enough to enter.