Scratch is a tool created by the MIT Media Lab for game creation, targeted at an introductory level yet capable of much more. If you want to put any games you made with it onto GameJolt, here's the basic steps:
Create a .zip file. The name doesn't matter.
Go to the project you want and copy the embedded code for it.
Paste this code into a new text file. Save this file as "index.html"
Put the "index.html" file into the .zip you made before. Save the .zip somewhere you can find easily, we will need it later on.
Then on GameJolt, create a new game by clicking on your icon in the top right and clicking "Add Game".
You will first go to a page asking you to agree to a bunch of stuff, read it and press accept rules.
You'll then be put to a page where you fill out the game's name/site/genre/engine/description and other things. Fill all of this out and then click "Add Game" at the bottom.
You should see your game page now. There's a lot of stuff to fill out here, but I'm just going to focus on how to add your game file in this tutorial. To do this, click the "Builds and Files" button.
From there, press "Add package"
Then press another "Add package" button. You can also fill out the description/change the title (not recommended) for your package here, if you are interested.
Now press "Add release" and then "Save Release"
Now click "Add New Build" (so many buttons to click .0. )
Now a screen with all the different types of downloadable games will come up, but our game is played in the browser, not downloaded. Click "Browser."
Alright, now we actually get to upload the game. First, make sure that you are set to "HTML" since we are embedding the project with HTML Iframe code. Second, under "Upload File" click "Choose File" and navigate to the .zip you made earlier. Third, you need to set the width to 485 and the height to 402. Once, all that is done, go ahead and press "upload build."
You may have to wait a while for the file to process. Once it finishes, you should see a button that says "Publish Build." Click that to make the game visible to people besides you.
And you're game is done! Now all you have to do is fill out the rest of the page and then actually make the page visible. There are other tutorials for how to do that though, the goal of this one is just to explain uploading Scratch games.