There's an instructions spot directly above where you had to type in your comment. That ammo is for seeker rounds... You have unlimited ammo for your regular weapon. The down key is fire. Left and right strafe and AWD move forward and turn.
I hate to leave negative feedback, but you contributed basically nothing to the development of this game. It's someone elses kit and graphics. You added some spikes and did some bad level design. Next time use at least some simple custom graphics. It could have been pretty good.
The controls are very difficult. For some reason I couldn't shoot until about a minute in. Overall a decent attempt. Maybe don't release so soon next time.
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i am upgrading :)