Ok, if you want to learn then you should start by doing this your own.
What you need is
-a form to create / edit existing entries (pure HTML, maybe +JS; depends on your needs)
- an output (ideally generated by php) page
- the script itself, that handles input / ouput / storage
at first you can decide, if you have one script handling everything or splitting in to simple scripts.
Next thing is on thinking about how to read data from a form, and how to handle files. But be aware that it is much easier to store data into a database (also the syntax / code is not really complicated) if you expect multiple parallel accesses to the data. Cause to change the data, you have to read the whole file, change the selected dataset and store everything (!) back.
To read data from a form / a http request, you take the superglobals $_GET / $_POST / $_REQUEST (combines POST + GET). If you do not know anything about arrays have a look here : (http://www.php.net/manual/en/ref.array.php
For filehandling you should take a look at www.php.net
for the functions
fopen, fgets, fputs, fclose.
Also take a look at is_resource to handle errors (or the "or die ..." - construct)
If you store the data you should think about marking each field with a sign, e.g. a colon etc.. so you need to split the read string as well as convert the data to such string.
Herefore the functions split, explode will be helpfull.