Different types of strings can be used to create different sounds and feels. Round wound strings are the most popular strings for slap bass playing. The gauge varies between light, medium and heavy. A standard medium gauge would probably be the best to start with e.g., G = 45, D = 60, A = 80, E = 105. The heavier or thicker the gauge the "bigger" the sound will be.
The lighter the strings the easier and faster you can play. Always clean your strings with a cloth after playing as this will keep the sound brighter. To get an optimal sound, and if you can afford it, change your strings several times a year, especially before an important session or recording.
The easiest and most accurate way to tune your bass is by using an electronic tuner. An electronic tuner allows you to tune each string individually to the tuner, by indicating whether the notes are sharp (too high) or flat (too low).
You can plug your bass directly into the tuner using the same lead that plugs into your amplifier. There are several types of guitar/bass guitar tuners but most are relatively inexpensive and simple to operate. Tuning using other methods is difficult for a beginning bass player and it takes many months to master. So we recommend you purchase an electronic tuner, particularly if you do not have a music teacher or a friend who can tune it for you.