With school out and the summer jobs starting be sure that you fill out your W-4's for Federal and State as well as the I-9. If you are not provided these forms, ask for them.
If you are working a job that the taxes are not being taken out, you may be considered self-employed. Types of jobs for self-employment can be baby-sitting, mowing lawns, delivering newspapers, ect. Such earnings if over $400.00 will be liable for self-employment tax as well as Federal and State taxes.
Also, tips you receive must be reported to your employer if over $20.00 a month. Tips are considered taxable income and must be reported on your tax return. In some cases, tips will be reported on your W-2 at the end of the year.