How can the facet function in ggplot be used to create a histogram in order to visualize distributions for all variables in a dataset?

This is an example of the variables that I would like to visualize

id  post.test.score  pre.test.score  messages  forum.posts  av.assignment.score
1        0.37             0.48         68          7               0.19
2        0.52             0.37         83         22               0.28
3        0.42             0.37         81          7               0.25
4        0.56             0.34         94         14               0.27
5        0.25             0.39         42         11               0.07