If your porch is not wire for light, you probably do not want to use it after dark. Unfortunately, installing porch string lights on a porch usually requires hiring an electrician, which can be expensive. One way to clear up your porch at night without the need for wiring for lighting is to put the chain lights on. Chain lights are easy to install, they are cheap and install to an indoor electrical outlet. Measure the perimeter of the room to determine how long your string lights need to be. If you plan a string of lights along the inside of the porch roof, measure a length and multiply it by the number of lines you want.
For porch string lights that will face the elements for years, consider obtaining commercial chain lights. These are more expensive. But they also come in long strands and are create for durability. To keep the light wires from getting tangled as they hang, keep them in their package until you need them. Be careful not to overload the outlet with too many chain lights. Avoid connect to anything else at such a point of sale, and check how many watts lights are being remove. The total number of watts is divide by 120 volts (typical in a US home) to determine the amps. Try not to go more than 15 amps per circuit for your porch string lights.