Listed here are the various ways you can find the list of transaction codes and their usage:

Use transaction SE11 – ABAP Dictionary:

Fill in the Database table name and click the Display button.
– TSTC table will contain all the Tcodes and
– TSTCT table will contain all the Tcodes with Texts.

Once you entered the screen, click in Top Menu – Utilities – Table contents – Display

If you want to display all the transaction code (total – 57,048) you have to change the Fields: Maximum number of hits to 99999 (default 500).

or

Simply goto transaction SM01, although this tcode is to Lock/Unlock any transaction code, you can also view all the tcode available in the R/3 system from here.

or

Goto transaction SE93

There are two ways where you can find the list of transaction codes in SE93.

Method 1:
You must be familiar with the starting characters strings for each of the R/3 application modules.

Assuming you know that most Materials Management transaction codes start with MM.

In the Fields: Transaction code, type in MM* and press the function key F4

The list of transaction code starting with MM will be displayed.

Method 2:
On the Top Menu, click Utilities – Find – Execute and the first 500 transaction will be display.

If want to display all the tcodes, make sure you remembered to change the Fields: Maximum no. of hits right at the bottom of the screen.