As Joe mentions, you can type in calls to the Unit() constructor. That accepts full wordings, as well as abbreviations and SI prefixes.
Another entry mechanism, which can give you the nice 2D Math typeset for for both your input as well as your output, are the two (SI, and FPS) unit palettes. Both of those two (Standard GUI, left panel) palettes have a top-peft entry which looks like [[unit]]. When you select that entry with the mouse-cursor, the GUI inserts a placeholder at the current position in the worksheet. That input now shows the 2D Math brackets also used for representing units in output. You can type whichever valid unit value you wish inside those double-brackets.
Yet another entry mechanism for obtaining the prettyprinted [[..]] form of units within 2D Math input is command-completion. For example, on MS-Windows, typing in the letters Uni and then simultaneously the keys <Ctl>-<spacebar> will result in popup menu. The third item on that menu is the typeset holder for entering units (and which works just like the described palette entry).
You can also invoke the Unit contructor (typed in, or via the palette) with an arithmetic compound expression involving unit names, eg. 4*meter+5*inch. The result will be automatically combined and output using the base units of the current system (default: SI).
You can see the spellings, abbreviations, and prefix which Maple accepts for the 'tesla' unit by issuing the command
Units:-GetUnit(T);
You can see which SI prefixes Maple understands for use with units on the help-page
units,prefixes
