Depending on the job it may be fraud, and therefore illegal. It's more likely to be a criminal law issue if you pretended you had professional qualifications for a job where these were mandatory (eg pretending to be a doctor when you're not), or if your employer is a Government agency. However, if all you lied about were your school qualifications, then it's not likely that an employer will involve the police. They may, however, sack you and, what's worse, give you a bad reference, in which case it can stop you getting jobs in the future.
The problem with lying about school qualifications is that people will probably ask to see your diploma or other proof of schooling before you start the job. If so, then you won't end up getting the job.
If you are lucky enough to get your first job through these lies, do a really great job, get a really great reference and you won't have to pretend for your second job!
A better way is to get advice about how to properly apply for jobs. Maybe it's not just your lack of qualifications that stop you, but also the way you present yourself. Get someone to help you write a good resume and letter to the employter. Pay attention to details like spelling and try and find out what an employer wants. If you're very motivated and really want a particular job, offer to work for free for a few days to let the employer try you out, but don't get upset if they then don't take you. Ultimately, your work has to speak for itself. If you do a good job, in a few years, people won't care how well you did at school.