Import means bringing information into an app, often from a file. Export means saving information out of an app so it can be used somewhere else.
For example, you could import a spreadsheet of contacts into an address book, then export the updated list as a file to keep a copy or move it to another tool.
The two apps need to understand the file's format, such as CSV, for the information to line up correctly. Before importing, check that the file is the right one; importing the wrong data can create confusing results.