Go to link A in the description.
Find your Minecraft version on the right.
Click "Windows Installer" under "Download Recommended".
Click "Skip" in the top right corner after 5 seconds.
Save the file.
Go to link B in the description.
Find your Minecraft version (could be on the other pages).
Click the gray download button.
Save the file.
Go to link C in the description.
Find your Minecraft version (could be on the other pages).
Click the gray download button.
Save the file.
Open the Forge installer from link A.
Leave the setting as "Install client" and click OK.
Once the Success window pops up, click OK.
In the Windows search tab, search for "%appdata%"
Double click on ".minecraft"
Double click on "mods".
If you see a folder with the version you want to install Schematica in, double click on it.
If you do not see a folder with your version, create a folder with the version you want. In this example I created a folder for the version 1.12.2
Drag the other 2 files into the version folder.
Launch Minecraft
Go to "Launch Options".
Click on "Add New".
Open the Version tab and scroll down till you see the Forge version.
Name it whatever you want.
Click "Save"
You should now see it at the bottom of the version list.
Click "News".
Open the green arrow next to Play and scroll down to the Forge version.
Schematica is now installed.
