Functional programming looks at programming like a function in mathematics. The program receives input, together with some information, and uses this information to create output. It will not have a state in between, and it will also not change things that are not related to the computation.
Procedural programs specify or describe sets of steps or state changes.
Stack based languages look at some of the program's memory like a stack of cards. There are very few things that can be done with a stack. A data item can be put on the top of the stack. This operation is generally called "push". A data item can be removed from the top of the stack. This is called a "pop". You can look at the item at the top of the stack without removing it. This is called a "peek". If a program is written as "push 5; push 3; add; pop;" it will put 5 on the top of the stack, put 3 on top of the 5, add the top two values (3 + 5 = 8), replace the 3 and 5 with the 8, and print the top.

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