Enantiomers are stereoisomers that are mirror images of each other.

eg. 1:

1 and 2 have the same molecular formula and the same structural formula and, therefore, are stereoisomers.  1 and 2 are mirror images of each other.  Thus, they are enantiomers.

eg. 2:

3 and 4 have the same molecular formula and the same structural formula and, therefore, are stereoisomers.  3 and 4 are mirror images of each other.  Thus, they are enantiomers.

eg. 3:

5 and 6 have the same molecular formula and the same structural formula and, therefore, are stereoisomers.  5 and 6 are mirror images of each other.  Thus, they are enantiomers.

see also diastereomers