What are the coins used for?

Coins are used to get into one on one matches, each stage costs a certain amount of coins..ex. Stage 1=400 coins buy in but if you win you get back 800 and a chest with more coins and important gear. The higher the stages you unlock the higher the amount of coins you have to wager, but if you win it's worth it. You have to win a certain amount of trophies in each stage to open the next and move further in your game..Becareful of losing too many matches because you also lose trophies from the stage you're playing. I found it best to stick to lower, cheaper games until I got the hang of the game since there is no practice stage.

Dani Marie is incorrect about Stage one, its 100 to enter a match, but winning gets you back your fee and gains you the opponents fee when you win, thus the total is still tallied in whole toward the winnings for ranking up to higher brackets. Still you have to play at the stages you can manage to gain more than needed for the next Stage in order to open the next one as required. Also they help to upgrade the equipment, again this is dependent how much you can win as what you spend on upgrades you now have to regain in winning matches. TO see what equipment you have in the bottom of the Stage selection on main lobby to the left side is the Equipment shop, it should show a number depending how much equipment you have which are ready for and needs upgrading, but again as said before, only upgrade the equipment when you can spare the coin for it, and the costs increase dramatically each time as you upgrade items. Tees are not upgrade-able and only obtainable through replenishing or purchasing with gold or real cash in the store (in my case I get Wind I and Power I for free by watching (just playing it really) a video ad. Do Not go for the Free option on the other groups of gear where offered, they either do not work or not offered for real or otherwise could be phishing scam so DO NOT waste time with those offers..