If you want to start painting, you had better have some knowledge of colour theory, at least some basic one. Well, you could buy lots of different colours and use them as they are, but that would be very expensive and not practical.
With just the basics you can already tweak your standard colours a bit. Want your red more orangey? Mix it with a little yellow. Want to make violet from your blue? Mix the blue with a little bit of red. And there is nothing wrong with already having a green and an orange and maybe also a violet in your palette. And some browns. With this you already have quite some options.
The next step would be to understand that there are warm and cool versions of basic colours. A warm red leans towards orange, a cool one towards violet. A warm blue leans towards violet, a cool one towards green. A warm yellow leans towards orange, a cool one towards green. If you want to, say, mix a good, brillant violet, mix a warm blue and a cool red. They both already lean towards violet. If you do the opposite, you get a quite muddy colour.
It can also be helpful to know that you can tone down colours by mixing them - carefully- with their complementary colour, for example put a little bit of red into your green. The resulting colour is a less saturated, that is a less brilliant green.
With this knowledge you can experiment with your paints and see what you can come up with. Mix a warm yellow and a warm green and enjoy the colour you get.