Sativa is a classification of cannabis known more so for its energizing and uplifting effects. People tend to use sativa's more when they are doing an activity during the day or at a sociable event.
Indica is a classification of cannabis, known more so for its relaxing and sedating effects. People tend to use indica's more when they are done with the day and winding down, or right before they go to sleep.
50/50 hybrid is the last classification of cannabis, which means it is half sativa and half indica. The effects of a hybrid are right in the middle of the effects from a sativa strain and an indica strain.