To begin the process, you must first find a texture pack that you like and would wish to install. There are multiple websites online that offer a variety of texture packs. Some sites that you can check out are CurseForge and MinecraftTexturePacks.com.
Some texture pack creators even have their own websites dedicated to their texture packs. When installing a texture pack, make sure that you select the version that corresponds to the one that you will be using in the game, as some texture packs only work in specific versions.
Once you have downloaded the texture pack of your choice, you can go ahead and launch the game.
After launching the game, select Options, and then select Resource Packs. Now, click on Open Pack Folder. This will lead you to the resource packs folder, where you can place any texture packs that you wish to use.
Next, just drag and drop the texture pack that you want into this folder and go back into the game. After doing this, you will see the texture pack that you added is now displayed on the left under the category of texture packs that are Available.
To use a texture pack, all you need to do is hover over it and click on the right arrow that will appear. This will move the texture pack to the right under texture packs that are Selected. Click on Done to apply the resource pack. Now, you should be able to see the texture pack working in the game.
To remove a texture pack, go back into the resource pack in your game options and hover over the pack that you wish to remove. Click on the left that will appear and click on Done. That should remove the texture pack.
You can also use multiple texture packs at the same time, but keep in mind that some texture packs may not be compatible with each other, so you will need to make sure that you are adding texture packs that will work together.