At first, you have to open the MP3 or other audio or video file on which you want to apply an effect. To do that press on the "Open" button of the toolbar or select "Open" from the "File" menu.
You can also drag and drop the audio or video file to open it.
Step 2 - Select part to apply effect
Secondly, mark which part of the MP3 file you want to apply an effect.
You can do this by selecting the part of the MP3 file's waveform.
Alternatively, if you know the start and end time or duration of the desired part, enter the start time, end time or duration in the appropriate text boxes.
To select the whole MP3 file, press Control-A or click on "Select All" of the "Edit"->" Select" menu.
Step 3 - Apply Effect
Now select an effect from the "Effects" menu.
Then the effects screen will open. There you can specify the various options for the effect and finally press on the "OK" button.
Optional Step 4 - FFMPEG Arguments
You can also specify the FFMPEG command arguments of the effect directly by pressing on the "More Options" and then entering the arguments in the "FFMPEG Args" textbox.
To view more info on the effect and its arguments press on the "Effect Info" button
Step 5 - Specify Output Format Settings
Press on the "Output Format" button to specify various output format settings or leave the default ones.
Step 6 - Get the Result
Lastly, select "Save Whole Clip" from the "Cut" menu to get the result file.
In case, you want only a part of the MP3 file, after selecting it, you can choose also "Cut Only Selection" from the "Cut" menu.