STEP 5 - Ladder, CSF and STL. Also Graph 5 if you pay extra.
STEP 7 - Ladder, FBD and STL. Also Graph 7 and ST if you pay extra.
Ladder is the same as most ladder for other PLC's, except you do not have the range of advanced instructions as others.
CSF and FBD are AND and OR gate type graphical instructions, basically the same range of instructions as Ladder, you can have more in series though.
STL is almost machine code, this is where the power of the Siemens PLC is.
Advanced instructions, a lot of the advanced instructions you get with other brands built into the ladder language, you get with Siemens in the form of system blocks, that pre-written code by Siemens. With Step 5 you quite often had to pay for these, with Step 7 they are free and come with the programming package.
You can also build your own to your own special instructions if you desire, using FC/FB's and usually to get the true power programmed in STL.
Graph 5 and Graph 7 are graphset type languages, for sequences, where you have transitions and steps. I have used Graph 5 but never Graph 7. Some companies specify this type of language, in my experience Nuclear and Pharmacutrical.
ST = structured text, this is similar to a basic format.
The most difficult 'switch-over' when first programming Siemens is getting to grasp with STL, once you have managed this you will find Siemens one of the most powerful PLC's on the market.
Most that switch to Siemens, especially from AB, critisise the lack of ladder instructions (especially those instructions they get used to using in their favoured brand of PLC) and the difficulty of programming STL.
Simply Siemens is not AB or any other PLC and once you get over that prejudice and learn how to use it you find it easy and powerful.
Step 7 has added some of the 'missing' instructions, such as one shots.
Siemens is not perfect, but neither are t6he other PLC's.
Some operating advantages of Siemens I have found, the tools are built into the STEP 7 programming language.
No RSLinx equivalent, its not needed.
You can compare programs within STEP 7 you don't need a seperate program to compare and you can compare online/offline. You can go on-line with a program that is not identical with what is in the PLC.
You can build tables to monitor the range of variables you want.
To be fair there could be long lists for and against Siemens when comparing to other PLC's.
It is one of the best on the market though.