Hi Bert,
As the laser bar meter increases so does your firing rate (so you can fire more shots at enemies). Every time you go up to a new weapon level (which fires more bullets) you have to increase the laser bar meter some more to recover your firing rate.
The power meter (to the right of the laser bar meter) increases the damage your weapons do to the enemies. At the start of a colour zone one shot will destroy an enemy, but as time goes on enemies 'Level Up' and take more shots before they die. Powering up the weapons makes it easier to destroy them.
As for the weapons, they are pretty different, in the full game you have weapons such as shield which makes you invunerable for a short time. You can also freeze all the enemies on the screen or use the orbit weapon to try to destroy any enemies that come close.
If you take a look in the Help section from the title screen you will be able to find more information about the different meters, the weapons and the enemies.