How to set album picture

Hello! Apologies in advance if this has already been asked, but when uploading new patterns, how do I set the thumbnail preview image? T-T

Turquoise

Image section... But right now there is aproblem system says "error" but uploading is get done  ... Only big than 1 mb pictures can not upload on the system ... Just for info ...

If I am misunderstood please give more detail on your problem ... We can solve :D  

aprilknits

Tysm for taking the time to provide such a detailed response <3 I just realised how poorly worded my first post was, so sorry!!! When adding images to posts, is there a way to set the thumbnail of the thread as well? So that when it appears in the relevant forums, the image is shown~