Simple Game Problems

I’m quite stumped on this and cannot find any references on the internet about it, or my search skills or horrible.
Anyways, I need to find out how I would make the “virus” which is the grey blob on the third frame to appear randomly around the circle in the middle and start to move slowly in a gravitational manner where it isnt going straight at it but maybe go near it at an angle or shake while doing so, and make the circle able to shoot those “viruses” or… if a virus makes it to the middle to activate one lost life.

Please help, I want to actually make a simple game without giving up.