i found some pretty cool mods on youtube and decided to buy and play it modded, but when i finish mod, the game have some crashes, glitches, and some mods never shows up. is ther any tips when modding, or is there any need to apply mods 1by 1not just dump them randomly?

Need more info on yer set-up. Are you using a mod manager? if not i would recommend you do, it's ALOT easier that way, just make sure you install it in the same directory as the EXE or else it does its best to mimick a spider in a bathtub and throw its self down the drain.

Ditto on using a mod-manager - Nexus is the go-to for Fallout (and many others). Some mods will require applying before/after others, though occasionally the modder will specify this - where are you grabbing the mods from?

I think you need to put some mods, like NVSE, in the same place as the EXE Manually. After doing some modding for Morrowind i found that Nexus Mod Manager didn't work for anything that says it messes with the scripts, like MWSE or MGE \ MGE EX, but mods that add models, textures, sounds, books etc... seem to work fine with NMM. Hopefully it works Similarly for New Vegas and this helps a bit.

I looked it up when i was having trouble and didn't find anyone who outright said "This will not work if you try to have MM do it for you."

So I'm going to say it to anyone who finds this and has the same issue.

If you try to get a Mod Manager to install anything that messes with scripts it will not work.

If you're planning to play Fallout 3 or Fallout: New Vegas with mods, the first think you want to do is download a mod manager called Fallout Mod Manager (or FOMM for short). You can also download the Nexus Mod Manager, as some modders make their mods specifically to be installed with that one (however, it is not as good or error-free as FOMM, and the Nexus staff basically abandoned it, so I personally am not too fond of it). After doing this, I'll need more context to help you, such as the mods you're trying to run, and how many of them are you trying to run. Bear in mind that some mods require the installation of third party programs like the New Vegas Scrip Extender (NVSE) in order to run.

Modding Fallout is relatively easy and simple, even if you want to do it manually and without mod managers, but then you'll have to double check if newer mods are not replacing old mod files (causing the old mods not work). There are also some mods that are bug/glitch filled and I would not recommend them at all since the creators have stopped patching those issues (one example of this is Fallout Character Overhaul, which looks great but is so full of bugs and conflicts that it is simply not worth it in my opinion).

Anyway, feel free to PM me if you need direct help with mods, I'll do what I can do clarify things for you and walk you through some of the installation processes.