Assembly language - More than one type?

There are many, many types of assembly languages. The current most popular are ARM, MIPS, and x86. ARM is used on lots of cell phones and many embedded systems. MIPS is popular on IBM CPUs and is found on systems such as Macs, some video game consoles, and a few I'm sure I'm missing. x86 assembler is used on Intel PCs. Each flavor has different versions which span the gammut from 16-bit to 64-bit instructions. The thing about assembly is old architectures tend to die and new ones come along, but the fundamental things that RISC style systems do are mostly the same. It's just a matter of learning the mnemonics between systems. Move, Mov, Load, etc. all load a register with a value. It's like any other language really. Once you learn one, it's pretty easy to pick up newer ones. Some older ones you might run into are Z80, 68000, 6502, and 6510 - depending on how far back in the way back machine you want to go.

Hope that helps.

but don't know if there is more than one 'assembly language'

Different assemblers (e.g. Gnu's and Microsoft's) for the same CPU may have different assembly language syntax; but the difference is trivial, because they're both targeting the same CPU, and there's a 1-to-1 mapping (if you ignore macros) between assembly instructions and CPU opcodes.

The bigger difference is between different types of CPU.

Sometimes different CPU support the same opcodes (and can therefore be targeted by the same assemblers), because they're designed to be compatible with or competitive against each other, by executing the same machine language.

But sometimes they're different: see List of Instruction Set Architectures.