What amount of taxes should I be taking our of my paycheck? (& other ?'s)?

I am considered self employed and they do not take taxes out of my checks. I need to know how to determine the amount I need to take out. For this job I only make about 2500 a year...do I even have to take taxes our for that amount? If I do not take them out during the year, how will work come tax time? My hubby and I file jointly if that matters. Thanks so much ahead of time for any answers!