There are seven chakra centers but not all can be opened while meditating. The root chakra for example can only be opened during some sort of physical activity. The sacral chakra (for feeling and sexuality), the navel chakra (for confidence), the heart chakra (for love and caring), the throat chakra (for self-expression and communication), the third eye chakra (for insight), and the crown chakra (for wisdom and connection to the universe) can all be opened during meditation.
Each chakra requires a specific set of ideas to focus on during meditation. Each requires practice and time to perfect in order to open your chakra centers.