I personally use PicMonkey for all my youtube art, whether it be the channel art or the thumbnail its my go to i usually use transparent pictures from google or use the eraser tool to take out the background like i did for my LeBron James video though sometimes that can be difficult. I would definitely recommend this site, it is free however has premium features, however i use the free version and it works fine for me. They're tons of videos on youtube for how to use it even though its pretty self explanatory i would incorporate your channel name into the channel art and then put up the social medias you have and put transparent pics of each of their logos, you can check out mine for an example, i have my socials and then the at sign with my handle. It does take time to create a good looking channel art and thumbnails but its totally worth it once you make something that looks great! Hope this post helped, go make those awesome banners and thumbnails!

side note: i think when i made my channel art for my banner i had to adjust the size when i saved it on pic monkey you can adjust the size on the "save" screen, i cant remember the size i had to use, it took a few times to get it set right but i believe that it tells you the size it needs to be on your banner edit/upload screen on your channel.
We love using picmonkey! But, for adding words, we also pixlr which we create our titles in with a transparent background, and then upload it to picmonkey as an overlay.

Julia and Claire
I find it so much easier to use photoshop :D, i know where everything is and i feel like have more control over everything on it :) i did use Panzoid at one point when i wanted to make quick thumbnails but ive dedicated more time into making better thumbnails for my gaming videos :)