How many days a week is good??
Laura, you have already been answered... The thing I'd like to point out is that it's very important to let your muscles have rest. This could happen even only training different muscle groups every day (there are a lot of people having only one rest day per week), but I think you're a beginner who is targeting abs so I'd recommend 3 days a week. If you go to a gym they would say Monday, Wednesday and Friday rather than Monday, Tuesday and Wednesday for a reason. You should let your muscles recover, that's when they get stronger. Of course a lot depends on the workouts as well. On rest days you can still have light cardio, stretching, walks... That's called "active rest day". It's your choice. In my opinion you should try different solutions until you find the one that suits you. Good luck! :)