zip file you downloaded in the first step to the newly opened 'resourcepacks' folder. – folder titled 'resourcepacks' will pop up
On the options menu, click 'Resource Packs.'.Launch the game client through the Minecraft launcher.– if there are many different versions, just choose the one you like, is compatible with your version/edition of Minecraft, the one you think your computer can handle in terms of performance.
– general recommended step for all packs, Optifine is also needed for most shaders
