Optifine is only required for HD texture packs; it is not required nor necessary if you don't use/have any installed to your texture packs folder.
ModLoader/Forge is needed for some mods, but not all; it's best to consult the mod's topic and read the requirements to be sure whether or not the mod needs either mod loader installed.
Lots of mods do not need forge, big ones such as: OptiFine Too many items and Better Sprint (all i know of)
No, only when you download them the first time.
This depends on if you're lagging or if you need a patch for it. If it's lagging I recommend installing optifine to your minecraft.jar folder. If that's the case google "Optifine download and installation tutorial" If you need a patch and it's just wierd lighting glitches or delayed block breaks, at the sign-in part of your minecraft client, click options and turn on force update. It will delete all mods but it will fix these glitches. You're welcome if this helped :) -youtube.com/user/DjOver9000
You NEED to have downloaded minecraft to use mods. There are hundreds of mod installation tutorials for all of the most popular mods on YouTube!
Mods (modifications) are free. You do not need to pay, however, you do need to be able to download them. Use Magic Launcher or Forge to do this.
Mods can usually be downloaded from where they are publishedSome mods come with an installer to install the modFor other mods, you need to install them manually by opening the zip file they are in and copying the contents to the minecraft.jar file found in the bin folder of the .minecraft directory
Press CTRL but you need the mod optifine to do that
to download the mods, no, but to actually install them you need some form of an archiving program that can convert files into .zip or .rar format
Optifine is completely free to download. If you need help installing it look up youtube videos how to install it
You need to download a mod, search Minecraft plane mod
NO!
You cannot zoom in on vanilla Minecraft. You need to install the Optifine Mod for this feature.