There are two generally recommended grip techniques.
Both have an emphasis on aligning your middle finger with the centre of the bowl to help with a straight delivery.
There are different grips on the bowls with different names but mostly come down to dimples or channels. The depth of the channels can change the feel significantly
Top Tip: Do not buy your first bowls or change bowls without trying the grip type first. It can feel very different and may not suit you. The shop will let you try them if they have them and if you are thinking of trying something a fellow bowler uses then they will often be kind enough to let you have a quick go to see how they feel.