Here you will find all of the tutorials that i made myself. if you have any questions please email me at plastic0crow@gmail.com (feel free to make requests too!).
Here's how to make a stamp with the free editing service Photopea:
Find and download stamp template with a transparent background. you can use this one below:
Go into photopea and open the file.
Click the Rectangle select tool (or hit M) and make a rectangle the size of the content space inside the stamp. It should measure at 91x47 pixels.
Click File at the top of the screen and press "Open". Open the file you want to make into a stamp. (If it's a GIF file, please continue on this tutorial. If not, crop your image to 91x47 and duplicate it(right click) into the original stamp file.)
On the GIF file, click Edit, click "Free Transform", and then change the width of the image to 91px (make sure you are clicking on the FILE, not the individuial image!)
Duplicate into stamp template file and use "Free Transform" to adjust the image
Make a 91x47 selection with the rectangle select tool again
Go into Layer and select "Raster Mask" and click "Reveal Selection" (also make sure that you are adjusting the whole GIF file!)