How can I combine two files into one bigger file?

Make the following in order to combine two files together:
Import both files into Audacity.
Select the second one by clicking on its label (the area around the mute/solo buttons).
Choose "Find Zero Crossings" from the Edit menu.
Choose "Cut" from the Edit menu.
Place the cursor by clicking in the first track, after the end of the audio.
Choose "Paste" from the Edit menu.
Play the audio file in order to hear the results. If you want to save the results, use the Export commands in the File menu.