How do I use agar plates?

We did something similar at university.
You divide the plate of agar into  sections (draw on the bottom of the plate).  
You can make little circles of filter paper...use a hole punch to get them all the same size. Soak several pieces of paper in your antibacterial prouduct (for the same period of time) BUT make sure its not soaking wet, dry it off on some paper towel.

You should culture your plate with bacteria (SAME SPECIES...so use the same colony...you should get a plate, swab it, let it gorw, get 1 colony and put that on anther plate and let it grow so you only have 1 colony and use it for all eperiments).

So culture your plate with bacteria (all over) then put on a piece of paper in a section of plate (eg in quarters so you have 4 products per plate). Then once you have let it gorw lok for the clear patches around each little circle...ie measure it.
Obviously you will need to repeat this so you have repeats and you can also play with concentrations as well...how dilute does your antibacterial need to be to be effective.

Normally, you should heat the agar and pour it into a petri dish while it's still warm. While you are doing this, try to keep it sterile by lifting the lid no more than you have to over the bottom of the dish. Then let it cool. Afterwards, you will pour the bacteria culture onto the agar. Using a spreader, gently spread the bacteria over surface of the agar. Be careful as not to push downward. You'll only be pushing the culture into the agar and it won't grow.

Hopefully, this link will work for you.

I use agar plates at work/I learned the techniques in microbiology lab (college). Common techniques include spreading, streaking and swabbing. 1) If you use a spreader (google a picture of one), it's stored in ~95% Ethanol, then sterilized above a lit bunsen burner. The EtOH on the spreader will be aflame until gone, then allow the spreader to cool. Meanwhile, pipette an aliquot of broth culture onto the plate. Once the spreader is cool, move the spreader back and forth on the plate with one hand, while turning the plate with the other, distributing the culture evenly on the plate. 2) Using a flame-sterilized loop, you can pick colony/liquid culture/frozen stock on the loop tip. Being careful not to puncture the agar, streak the loop tip back and forth (svereal times) across one corner/end of the plate. Flame sterilize the loop, and drag it through inoculated corner out to ~1/3 of the uninoculated area (stay near the edges) using a zigzag motion. Sterilize and repeat. Sterilize and repeat, only this time, zigzag the loop into the uninoculated center of the plate. Make sure the last streak does not contact the first or second one. 3) Swabbing is easy. Using a sterile cotton swab, pick an environmental/clinical sample and thoroughly cover the plate  with sample. Overall, it's much easier to demonstrate in person.