To cut the bottles you don't need to buy a special bottle cutter. This is how I cut bottles:
firsts you mark with tape and a paper strip where you want to cut the bottle, then put the bottle in a place where there is a 90 degree angle (example: where floor and wall meet), then with a simple glass cutter I press on the bottle and rotate it 360 degrees, in this step you do what is called the score line. The next part is where you actually cut the bottle; get a candle and heat up where you scored the glass. Some tips for this part, if the bottle isn't completely dry inside it will heat unevenly and if you heat up the bottle to much on the next step it will break. After heating the bottle you put the heated part in water. Repeat this process until the bottle break into two. If the bottles get irregular cuts the it might be due to uneven heating or a bad score line, something that helps is to lubricate the cutter and never score twice a sampe place.
When attempting to cut bottles alway wear safety gogles and be aware that glass is sharp and if broken it can cut you
When the bottle is finaly cut the edges will be sharp so you need to sand them, it is extremely recomened to wet the sand paper so the glass dust doesn't get into your lungs
or where a respirator. Start sanding the edges with a rough sand paper and gradually change to a sand papers of higher gritt.
Don't gett disapointed if your first bottles get cut iregularly, it takes some tries to get bottle cutting right.