Your are that blue sphere ship on that green thingy which is your base. The base is your safe point where you can rest. Touching a shot, the active cargo or a wall will destroy you.
The small green circles are cargo that must be carried back to the base. This is done by flying next to the sphere and pressing "T" to activate the tractor beam. While the sphere is inactive, you can touch it with your ship without being destroyed. Once grabbed with the tractor beam the cargo must be brought near to the base to be absorbed.
The sentinels will shoot at you when they see you. You can shoot back by clicking the right mouse button. Don't get shot und don't shoot yourself.
You can fly around by clicking the left mouse button next to your sphere ship. The ship will accelerate away from the left click.
The greyish area around the right cargo shows the aproximate tractor beam distance.