Can I share my buildings on forums? If yes, can I to do it trough .cw files? Or just post Images and videos?

Even if we most of us have the ClassiCube client, sharing them as a .cw file only might be a bit inconvenient.

What I'd suggest is posting an image alongside with a .cw file to the world.

What I'd also suggest is that you create a megathread for all your builds instead of making separate threads, but you probably should do neither if the builds are low-effort.