Drawing Lewis structures is a skill you learned in General Chemistry.  A brief summary of the rules for drawing Lewis structures is given below.  More details can be found in any General Chemistry book.

Rules:
1.    Determine the number of valence electrons in the molecule or ion.

2.    Place the atoms in a symmetrical arrangement with the first atom in the formula as the central atom.**

3.    Place a pair of valence electrons in each of the bonds between the central atom and the peripheral atoms.

4.    Complete the octets of the peripheral atoms.

5.    Place any remaining electrons on the central atom.

6.    If the central atom doesn't have an octet, form a multiple bond with a peripheral atom.
 

**This step can be difficult in complex molecules.  In organic chemistry, you will be expected to push electrons on structures given to you and thus generate a set of resonance structures.  You will not be required to generate a structure from a molecular formula until after you have been introduced to the atomic groupings (or functional groups) common in organic chemistry.