https://www.wikihow.com/Make-a-Minecraft-Texture-Pack has a step-by-step guide with photos if the page that bunnybisbyclyde linked you to isn't enough for some reason.

You can do an internet search for more pages that can help with making texture packs. It isn't really feasible for someone to explain how to make them here in the comments section. There is plenty of information online though.

If you are planning on making your own textures, paint.net is a great program (as bunnybisbyclyde said); you can also use gimp or photoshop. If you don't want to create your own textures from scratch you can do an internet search for free textures that you can use to make your pack...just make very sure they are free to use. There are tons of free textures online.

https://minecraft.gamepedia.com/Tutorials/Creating_a_resource_pack

Everything you need should be in that page.
Make sure you have an image editing program installed, something better than Microsoft Paint. Get something like paint.net, (getpaint.net). It is free, and there is a lot of stuff you can do with it.

Hope I was able to help!

plz tell me idk how