Use tile nippers or a hole saw designed for tile to cut curves.
How to cut tile on shower wall.
For exposed edges set edge trim or bullnose tile pieces in place.
Cut away large sections or large cutouts with a handheld circular saw equipped with a tile cutting stone blade.
Start at one end of the cut line and run the blade along the tile surface to the other end.
Spray water onto the tile when needed to keep the surface wet.
If your shower pan is not level then the level line you created to mark the top of the first row will mean that some of your tiles need to be cut.
Periodically check the tile line with a level to be sure they are straight.
Cut through the tile using an angle grinder.
Use bullnose for exposed edges or you can use trim pieces.
Hold the saw up to your marked lines.
Once only the bottom row is remaining remove the support board.
Use spacers between the tile to make sure the gaps are consistent.
Getting stuck and not having an answer well that s my biggest fear.
Or you can use a 4 1 2 angle grinder with a tile blade.
This tends to happen when homeowners need to cut a large hole in tile.
You could use a score and snap tile cutter or a wet saw with a diamond blade.
Use a tile cutter to just score the length of the tile and press firmly to cut.
Make multiple passes with the blade if needed to cut through the tile and to the subsurface.
You can buy a 3 or 4 carbide hole saw but they are super expensive.