How can you give an item a description in Minecraft in version 1.15?

I tried the command for 1.12 but it didn't work

Do you mean the lore (text under the name)?

If so, you have to go to http://mcstacker.net or others and then generate a command that gives you this item with the lore. At McStacker you have to click on / give and at giveitem you select the item that you want and enter the information you want at Lore halt. Goes colored, bold, and so on.

Goes 100%