The atomic number always tells you the number of protons an atom has.
For example, the element boron has an atomic number of 5. This means that all boron atoms will have 5 protons.
Because atoms are electrically neutral (no charge) the number of electrons must equal the number of protons.
Here is a video that provides a few more examples of how you can figure out the number of protons and electrons in atoms of various elements.
Hope this helps!