As with all software, make sure you are getting your mods from a reputable source. For most mods these days that means CurseForge, but for Forge itself you should only download from http://files.minecraftforge.net. Also if you are new please check out the StopModReposts project.
As for installing mods, any modern mod should require only dropping its Jar file into the mods folder Forge creates inside your .minecraft folder, the location of which depends on your Operating System, this page of the Minecraft wiki describes the .minecraft folder and where to find it on each OS.
Note: In general, if a mod requires an installer I do NOT recommend running that installer, I cannot speak for every mod but at this time I know of only two mods I trust that come as installers, Forge itself being one of them.