Download the Twitch App, and go to "Mods" then select a modpack from the list of packs there. Assuming you are attempting to "Create" your own modpack. There are thousands of modpacks already created and it is very likely you will find one with the mods you want. If Not, look for a Vanilla+ pack, and then unlock the profile, and add whatever mods you want. The App will make sure they are of the right version and what not. Thus you essentially create your own pack that way in a sense.