You can type assignments directly onto peaks in the spectrum. To do this, put the crosshair in Selector mode, and then select one or more peaks on the spectrum. Now, the normal keypress bindings of the spectrum window are skipped. Instead the characters you type are considered as an assignment of the peak. As soon as you start typing a yellow rectangle will appear on the window and the text you type will appear in the rectangle as shown here.
Assignment will not be done untill you hit the Return key. If you pause in this process for more than a few seconds, or hit the Escape key, the entry will be cancelled and the yellow rectangle will disappear. You can assign individual dimensions of the peak by separating the assignment labels with a comma. Typing "32.h" would assign the first dimension, typing ",32.c" would assign the second dimension, and ",,32.n" the third dimension. You can assign more than one dimension at a time: "32.h, 31.c,32.n".
The process works particularly well if you've set up an appropriate pattern for the peak list. For an hnco experiment you might have a peak pattern of "i.h i-1.c i.n" indicating that the first and third dimensions ard the amide proton and nitrogen of one residue, and the second dimension is the carbonyl carbon of the previous residue. In this example, you could simply type "32" followed by a Return and all three dimensions would be assigned to "32.h 31.c 32.n". More than one peak can be selected, so if you selected all the peaks in a vertical stripe of an 15N noesy and typed "32" then they would all have their direct proton dimension set to 32.h and nitrogen dimension set to 32.n
Sometimes you'll want to work in a spectrum window without this effect in action. You can turn off this behaviour by deselecting the "Extra key bindings" preference in the Spectrum Preference panel.
You can also use the Peak Identify tool directly from the spectrum. Just position the mouse cursor (in either crosshair or selector mode) over a peak (don't actually select it) and hit the i key. The Peak Identify tool will appear immediately to the right of the peak and suggest a list of possible assignments.