The amount of chemicals you need to add to your pool will depend on how clean it is and how regular you have been with maintenance. If the pool isn't very clear, it might need Super Shock to give it a heavy dose of chlorine. After that, it might also need algaecide and stabiliser.
Your pool pump, sand filter and salt water chlorinator need to be working well, so the rest of your pool can run properly. Check the pump is in good working order and water is flowing through the filter. Check the pressure on the sand filter. If it's high and the water flow coming out of the pool jets is low, it might need backwashing. If the salt chlorinator is covered in white scale, clean it in a hydrochloric acid mix.
Your skimmer box is designed to collect floating debris as well as connect to your pool hose. Make sure you empty it out regularly so the water flows freely through to the filter.
There are several different kinds of pool test kits you can use to test the level of chemicals in your pool. Always test your pool chemical levels after backwashing the filter. Follow the instructions on the kits to conduct the tests and add the recommended amount of acid or chlorine.
Standard pool test kits won't tell you how much salt is in your pool. After winter and heavy rain, you want to make sure it's at the right level before you go swimming. Use the salt test strip kit to check your salt levels. Follow the instructions on the kit and if needed, add as many bags of salt recommended for your size of pool.