Why does the page keep showing and I can't connect after I click "Uploa"？

Go to the “Upload” tab, select the file, and paste the source where you found it (it must be the original source and not from a third party or a paid content source). Add tags that describe the image, then click “Upload”—specifically, the blue button below it.

If it doesn't let you and shows a message at the beginning, it's most likely because the image is already here.

If that's not the case, I think you need a little more activity on the site (I'm not sure)

If the site won't let you upload images, then you may have to write some comments until your reputation is higher.
Less than 10 comments are needed to get the required reputation if I remember correctly.

Essentially, write comments until you can upload.
Read the rules about commenting and uploading before you do either.

gelbooru.com/index.php?pa...;s=&s=view&id=207
gelbooru.com/index.php?page=wiki&s=view&id=6645

1. Comment on non-work images to increase your reputation (this is meant to limit bots)
2. After a few comments you go to Upload
3. Click in select files and select the image you want to upload
4. Add the original source (twitter, pixie, DeviantArt, etc)
5. Add at least 5 important tags (big_breasts, solo, loli, foot_fetish, penis, futanari, etc.)
6. Press upload and wait until it is done.