Welcome! This guide will teach you how to add resource packs and apply them in Minecraft Java Edition.
Step 1: If you're in game, click ESC and go to options. If you're on the main menu, click Options.

Step 2: Click Resource Packs...

Step 3: Click Open Pack Folder

Step 4: Right-Click on the folder or .zip file and click Copy

Step 5: Go back to the Resource Packs folder, right click, and click Paste.

Step 6: Apply the resource pack via the arrow and click Done! The End! :D

Hope this helped! :D