There's two ways. One way is preferentially easier than the first.
The first way is to draw the compound, then next to it draw the mirror image. If you can mentally rotate one of them 180° clockwise, counterclockwise, or however, and cannot superimpose it on the other, then you know it is chiral.
The second, easier, way, especially for more complex molecules, is to use Cahn-Ingold-Prelog (priority) rules for naming enantiomers. An enantiomer is basically a chiral compound.
First by assigning what group is the highest priority, then what group is the second highest priority, and from there you follow the directions on how naming the enantiomer.
An overview of this method can be found
here.
If one compound is (
R,S) and the other (
S,R), you have a chiral compound. Likewise, if one is (
S,S) and the other (
R,R), you have a chiral compound. See a pattern here?
This takes some time to understand, because Cahn-Ingold-Prelog (priority) rules are paramount.