Hello. Ill give you a quick tutorial of how to do this, as i use optifine and damage indicators at the same time.
.
Step 1. Download
Forge
Step 2. Wait for that to download, then double click the .jar.
Step 3. A little page will come up, pick your settings etc.
Step 4. Go to your minecraft folder and find the "mods" folder within their.
Step 5. Download the mods you want and drag them into your mod folder.
Step 6. Choose your version of minecraft. One of them should say "forge".
Step 7. Play with your new mods.
.
Ps: sorry if this isn't helpful.. this is just how i did it