I have a couple of .esm mods like A World Of Pain and Project Nevada. I need help installing them into the game, I have fallout mod manager but when I go to install them by checking the box, the game always crashes. Should I use BOSS or something else?

Mod .esm files (masters) load right after your .esm files for New Vegas and the DLCs, and always load before any .esp files in your order. If you're getting crashes, you're probably loading an .esp file that's trying to reference an .esm that hasn't loaded yet. That will cause a crash every time.

Make sure you read the documentation for the mods you're trying to install. Large mods like AWOP and PN will give you load order tips to use with other popular mods.

I have Fallout Mod Manager and it has the .esm mods right below the main FNV .esm file. So should I check the box to install or rearrange the order of the mods because I have .esp mod files blow that checked and installed.

You should post your load order here on the forum - you may have a mod that's incompatible with the new ones you're trying to install.

So it's probably something wrong with the load order, ok I'll do that