see Protein NMR Spectroscopy – Principles and Practice by J. Cavanagh, W. Fairbrother, A.G. Palmer III and N.J. Skleton (Academic Press). (Link to Publisher)

Minimum labelling: 15N

Dimensions: 2

Magnetization is transferred from hydrogen to attached 15N nuclei via the J-coupling. The chemical shift is evolved on the nitrogen and the magnetisation is then transferred back to the hydrogen for detection.

HSQC magnetisation transfer

This is the most standard experiment and shows all H-N correlations. Mainly these are the backbone amide groups, but Trp side-chain Nε-Hε groups and Asn/Gln side-chain Nδ-Hδ2/Nε-Hε2 groups are also visible.
The Arg Nε-Hε peaks are in principle also visible, but because the Nε chemical shift is outside the region usually recorded, the peaks are folded/aliased (this essentially means that they appear as negative peaks and the Nε chemical shift has to be specially calculated). If working at low pH the Arg Nη-Hη and Lys Nζ-Hζ groups can also be visible, but are also folded/aliased.
The spectrum is rather like a fingerprint and is usually the first heteronuclear experiment performed on proteins. From it you can assess whether other experiments are likely to work and for instance, whether it is worth carbon labelling the protein before spending the time and money on it. Or if your protein is reasonably large you might be able to judge whether deuteration might be necessary.

HSQC spectrum