I finished cleaning my tuba, but I'm not sure where the springs go. I know they go into the valve but they are all different sizes ranging from largest to smallest. Does it matter what order they are in?
I have only once taken apart a trumpet before so I don't really KNOW the answer to your question, but since no one else has helped I'll tell you how I would try to get out of your predicament. Are the valve cylinders different sizes? The largest spring can't fit into a smaller hole, so I would try to find where the largest spring goes first, and then work to the smaller ones. Also the valves have to go back in the right spots and for that you might have to try to see where the tubes go to match the valves to those tubes. Remember the valves themselves will have a little key sticking out so they can only go in one orientation.
Aside from fit, another reason for the different size springs could be different weights of valves. The action is probably intended to be the same across all the valves, so a heavier valve will need a bigger spring to compensate and make it feel the same. If the valves feel different in weight, try matching the biggest spring with the heaviest valve.
Really what you need is someone who knows tubas to help you in person. I can only assume if you were taking lessons or a class you would have gone to your teacher instead of the internet. If you do have a teacher they are your best bet. If not, you should be able to get help at the store where you got your tuba or any store that sells tubas. I would call ahead first and ask them if they can help you put it back together. Lots of stores have maintenance services that they can sell you and you might get someone to help you out for free the first time.
Finally, you can reach out to the manufacturer and see if you can get some help in the form of phone support or instructions or something like that.