There are 3 things to consider when taking photos on a DSLR camera:
1.) Aperture- This controls both the depth of field by changing what would be in focus(depends on how far the subject is from what’s behind it) & lighting. If you want more aperture, you have to decrease the shutter speed.
2.) Shutter Speed-This controls motion depending on wether or not you want to capture a freeze frame or keep the motion of the moving object. If you want more shutter speed to get said freeze frame, you have to decrease the aperture. Like aperture, this also controls lighting.
ISO: This you have to keep as low as possible & should only increase when necessary, because this controls the light sensitivity.
You have to make sure all 3 settings are set so the exposure meter is set at 0, meaning the exposure is just right. The meter changes positions depending on the lighting of the area wether you’re outside on a sunny day or inside on a cloudy day.