The easiest way is to set it to auto and see what settings the camera picks and then adjust off that knowing what each setting changes.
For example - lower aperture numbers shorten the FOV (field of view) meaning that a smaller portion of the photo will be in focus. This produces the wonderful images you see of a single flower being sharp and the rest of the picture blurred out (bokeh) Larger aperture numbers will increase the size of this area, but will require extra light from other settings, such as longer exposure times.
ISO is the sensitivity of the sensor, higher numbers make it more sensitive to light and therefore able to take better pictures in low light situation, the negative side is noise, there will be odd random coloured pixels in the shot which may or may not lower the quality of the picture.