This tutorial is mainly how to fix errors you can get along with it.
Here is a simple tutorial on installing Minecraft Forge:
1. Setup MCP
2. Install ModLoader, and ModLoaderMP into minecraft.jar inside mcp/jars/bin/minecraft.jar
3. Decompile, and recompile. If it recompiles successfully then move on.
4. Download Minecraft Forge Source on the official thread.
5. Place folder forge inside your mcp folder
6. Run mcp/forge/install.bat then recompile
6a) If you get no errors when you recompile, you are good and can go and mod with MCForge
6b) In most cases you will get two problems when recompiling and they are
(click the spoiler to show error and solution)
Errors in Tesselator.java and other files
If this helped you, if could always press that + rep button.
If you have more to add, or get more problems I may answer them
Note: This is errors related to installing MCForge not errors when modding with MCForge, or modloader, or whatever.