I'm trying to create an image for my background but I'm not sure which dimensions to make it to fill the entire background on my profile, instead of having several of the same thing. please lmk. thanks!

The image is this: https://wallhere.com/en/wallpaper/1313159

The custom background images on profiles will appear differently, depending on the screen resolution of the viewer.
If you only want a single image to appear, choose the setting "no-repeat, and choose a matching background color.
Keep in mind that the maximum allowed file size for the background image is 1MB.

For example, this is what your profile looks like right now on my screen:
https://i.imgur.com/F4gH5wr.jpg

This is what your profile would look like on my screen if you used the 2560x1440 version of the image you linked:
https://i.imgur.com/FSRIJdg.jpg

However, the 2560x1440 file is too large in file size, it would need to be compressed, or you would need to choose a smaller image.
Generally speaking, if you want to the background image to fit for the majority of viewers screens, you should try to use a larger image, while not exceeding the 1MB file size.

That looks sick! How big is your monitor if you dont mind me asking? I guess the next question is, how do i convert it to a jpg,jpeg, or png file so that I can use it?

Mine is 3440x1440, but I am not sure what the most commonly used screen resolution is across most users.
I would assume many users will have 1920x1080, 3440x1440, 3840x2160, or 5120x2160.

You will have a hard time coming up with a custom background that looks equally nice on all of these resolutions and aspect ratios, you might as well settle for one that looks good on your end

If you need any help with converting, resizing, or other adjustments, feel free to PM me.

Can easily convert for you. Most of times you can convert them simply by downloading, reopening in lke paint or image viewer program, then save as, and change the format. I however have a photo editor program that i paid for for all my editing needs. I can do this super quick for ya If you are on discord shoot me a pm and can send me original, then i can convert for you