Aight first you need to go to this
link. When you do you should arrive to a page that looks like this.
Look for the bright green button at the top right that says "New Campaign". Click on it, and it should pop up a new window. It'll ask for a title and a description, though you only need a title. Put something that'll make it easy for you to find and understand what it's for such as "Gaia Frontier". I'd also recommend that you add a link to the RP just so you know where these rolls are suppose to go.
Scroll down a bit more and you should see a blue Submit button. Press that.
It should bring you up to a new page that would look like this. Notice how you don't have anything here yet, and that there are two empty boxes underneath the big words that say "New Roll".
The one labeled "Roll" is where you'd put in your die rolls, such as a 1d20, 2d6+3, and so forth. It is important that you put something for the first number represents how many dice you're rolling; the 1 in the 1d20 means you're rolling 1 dice. The number that follows the letter D represents how many sides of the die you're rolling, or basically any number between 1 and whatever you wrote down. It can be anything like a d4, d50, or even something weird like a d719. Though for the most part you'll be using a 1d20, though it may change depending on what you're doing or what items or abilities you're using.
The next box is a note to label your roll. While you could leave this blank, I find it easier to fill it in with something simple to describe what the roll is for.
This is an example roll. A 1d20+4 for Athletics. Say you're doing something like push ups or something, which would be an athletics check. because it's a skill check, you'll be using the 1d20 die, plus your athletics modifier. Athletics is scaled off your strength which is a +3 and because you're proficient with athletics you can add your proficiency, which is a +1. Thus, 1d20+4. Another thing to note: when the button is green, that means everything is good to go. If the button is red, that means you did something wrong in the roll section. For example, perhaps you forgot to add a number in front of the d20. If you don't add anything it won't know how many to roll. Or perhaps you accidentally put nothing after the + sign or put a space between the + and the number. Double check your work.
When you press the green button that says roll, the page will refresh and you should have something underneath the section that says Rolls (Newest to Oldest). There you can see the results of your roll. First you'll see when you rolled it, the die (In this instance it's a 1d20+4), and the Total Result. Next to it is a Note that specifies what this roll was about.
If that's all you need, you can click the Copy button. That will automatically copy a link to that specific roll to your clipboard so you can paste it into the RP. Alternatively if you want to see what exactly you rolled, you can click on the ID number.
This will bring you to a new page where you can see exactly what your dice roll was. The Constant is the bonus modifier that was added after the roll. In this instance, I rolled a total of 16 for the Athletics check: 12 on the 1d20, plus the constant of +4, for a total of 16.
It should bring you up to a new page that would look like this. Notice how you don't have anything here yet, and that there are two empty boxes underneath the big words that say "New Roll".