In order to input audio from a cassette into your computer, you will need a cassette player with a headphone jack, a patch cord with 1/8-inch phone jacks (these are inexpensive and available in any electronics or audio store) and a computer with a line-in jack (most personal computers have these; it may be separate from the headphone jack or combined) and a CD burner.
You will also need some basic audio recording/converting software and CD burning software. There are a number of free and inexpensive options that you can download, including Audacity, Blaze Audio and Gold Wave (see Resources for links). CD burning software generally comes loaded on any computer with a CD burner, as well as in audio programs like iTunes, RealPlayer and Windows Media Player.
Plug one end of the patch cord into your tape player and the other into your line-in jack. Put your cassette tape in the player and cue it up to the point you want to record.
Open a new file in your sound editing program and prepare to record. The recording toolbar on the program should have options to choose from regarding the audio source it records from. Make sure it's set to "line in."
Before you start recording, make sure you close all other programs on your computer that might create sound. Depending on how your audio program works and how your computer processes "line in" sound, you may end up recording other computer program sounds along with your cassette tape.
If possible, record your cassette audio by starting the tape, then starting the recording within the audio program, and stop recording in the reverse order. This will prevent any noise from the tape starting and stopping from ending up on your audio file.
After doing any necessary audio editing to remove silences or unintentional tape noises, convert your digital audio file into CD tracks using your sound editor. You may need to divide your recording into shorter files if they're longer than a few minutes each, but your audio software should have tools to help you do this (you can select, cut and paste audio just as with text or images).
Save your audio file and select MP3 as the file type. Once you've done this, you can burn the MP3 tracks to CD using your preferred CD burning program.