Trouble With Mods not being on server



I am installing FTB Infinity for my Brother and Nephew. I do not play the game but I am a computer tech.

I found the issue they are having here:

However, I cannot find what Yourself458 is talking about for a batch file to install the modpacks.

Furthermore, when I look in the server/mods folder it has all the mods in them. Is that the server mods or the client mods? The reason I am asking is when we load up the game it says the x mod is missing from the server. Where do the mods go for the server? and where do they go for the client?