There are several different ways to do this. This is one way that works.
satguru59 wrote:Song :1 Smack That - Akon - 5:05 minutes
Song :2 I am Feeling Lonely - Akon - 4:07 minutes
Song :3 Gasolina - 6:03 minutes
Track :4 New Created Empty Track
Import all the songs into Audacity. They will appear one above the other.
If necessary you can drag them up/down (click on the info panel on the left of the track, taking care not to click on the controls, and drag while holding down the mouse button).
Use the Mute and/or Solo buttons to hear one track at a time. See the bottom of this page for different ways that the Solo button can be configured
http://manual.audacityteam.org/o/man/tr ... ences.html The "Simple" behaviour will probably be most useful in this case.
satguru59 wrote:Then I may need to cut segments from Song :1
2:05 to 2:15, 3:20 to 3:35 ,4:40 to 4:46
Cut segments from Song :2
1:02 to 1:15, 4:00 to 4:07 ,2:40 to 2:49
Cut segments from Song :3
3:05 to 3:50
Select a part of one track that you want to keep. Press Ctrl+D to duplicate it to a new track.
Repeat for each part that you want to keep.
When you have all the parts from one track that you want, delete the original track (click the [X] in the top left corner).
Repeat for each imported file.
Ensure that the tracks are in the order that you want (top to bottom).
(The next version of Audacity will have "move track to top" and "move to bottom" commands, which will make this step more convenient. In the mean time, make use of the track "collapse/expand" commands to maximize your work space.
http://manual.audacityteam.org/o/man/view_menu.html )
satguru59 wrote:Concatenate ( Add) Song 1: + Song 2 + Song 3 into Track 4
Ensure that the first track starts at time = 0.
Select all (Ctrl+A)
"Tracks menu > Align Tracks > Align End to End"
Export your finished masterpiece

The tracks are mixed together into a single continuous file.
Optional steps - you may want to adjust the positions using the
Time Shift tool so that they overlap a little, then use the Fade In/Out effects to create cross-fades between the tracks.