To "attempt" to do something means to try:

We attempted to reach him earlier in the week, but were not able to contact him.

This example means that you tried to call someone, but you weren't able to talk to him.

The word "attempt" is pretty formal. Here are some situations where people use it instead of "try":

• You can use it in writing.
• It's common in legal writing and in court.
• Magicians use this word when they're performing a magic trick on stage:

  For my next trick, I will attempt to make this woman disappear!

• TV news shows and newspaper articles use it.