Flat tires are a fact of life for cyclist. Even if never ridden, perfectly good bicycle tires will go flat over several days due to seeping through the porous rubber of the tube. If your bike has been sitting for any length of time, the tires will need air.
Fill your tires to the pressure listed on the sidewall. Overfilled tires will ride badly and may blow off the rim. Under filled tires are slow and affect the bikes handling. Riding under filled tires can damage the rims and pinch-flat the tubes. It's okay to inflate the tires to the manufacturer's maximum recommended pressure.
Pinch flats, also called 'snake bites' are a very common type of flat that happens when you hit a rock, pot hole or other obstacle and there's not enough air in your tires. The impact pinches the tube against the metal rim. The tire will lose air instantly, and the tube will have two horizontal lines where the rubber has been cut. Usually, pinch flats are difficult to patch and sometimes the tube must be replaced.
for Flat Repair instructions