First of all you go to the forge and optifine page and download the version you want (must be the same version of minecraft in order to work properly)

Now here are the steps.

1: install Forge, after installed, theres no need to install optifine or the optifine and forge will be two options to select in the launcher you're using.

2: after install Forge, press Windows + R and paste this: %appdata% then, go to .minecraft and search for a carpet with the name of: mod.

3: if the carpet is not there, then just create it (with no capital letters)

4: paste or cut the optifine file inside the carpet and done.

5: if you have open the launcher during the steps, please re-open it to make a refresh in the versions of minecraft.

6: search the forge version you've installed and launch it.

and you finished, then wait a little to load, then play minecraft like the original version.

if you have some issues after install or launch the game, search for some help or see in youtube to find the problem you have.