I've searched "Full Width" in the wordpress Themes, the 1st one coming is "Fullscreen Lite Theme". " I've installed it, then it seems same (screenshot attached). Can you recommend a Theme for me? 

Thank you.

GeneratePress free is pretty versatile, the paid version even more so.

I've searched this Theme, it says I must install 2 plugins first, when I try to install their plugins, it says "Something went wrong with the plugin API.". I ignored it and searched it again, then it says: "No themes found. Try a different search."

Can you please recommend another Theme? Or I'm happy to pay some money and let someone teach me. I don't know how other people use this plugin?

Thanks.

@peterwangbiz, almost all themes have Full Width template for pages. You should edit forum page and check the according according option in right sidebar of Edit Page Screen:

In any case if your current theme doesn't have full width page template, i recommend filter themes on when you search for new one:

Thank You Very Much!

Peter