When it comes to cutting ceramic tile in a straight line there are really a few ways to do it. If you do not have many tiles to cut then you can use the scoring method. This would be a lot more suitable for a small tile repair or an extremely small job. It can be time consuming and frustrating so you would not have to cut many tiles to warrant using one of the methods mentioned later.
If you only have a few tiles to cut, use a straight edge to determine the line you want cut on. Then use a scoring tool to repeatedly go over that line. You will first create a groove and then deepen it. You then need to snap the tile. Resist trying to do this with your hands alone; try to use a wire or something flat that will apply pressure across the entire length of the tile. That will reduce the chance of breaking the tile in a place that you do not want to.
For most jobs you will want to use a tile cutter or wet saw. The wet saw can be relatively expensive for cutting ceramic tile, so it is probably not something you want to buy unless you plan to do a number of tiling projects. You can usually rent them, but you should be warned that they do not usually come with instructions. The wet saw has the advantage that you can cut tiles in a curved line. This may not be advisable though if you have never used one before as it will bring your hands close to the saw blade.
The tile cutter is a good option for many people. It does not take too long to get the hang of using it and not breaking tiles. If you want to minimize the number of broken tiles over the course of an entire job, you might want to take one as a tester and cut it many times until you start to get the knack for it.
If you are using a tile cutter for your job and you have one or two small circular cuts to make, you can buy a tool called a rod saw. It has a carbide outer layer and it fits into a regular hacksaw frame. It is labor intensive, it will work for cutting ceramic tile, however, you would not want to make too many cuts this way but it is an economical choice.