The querying (or ``resolving'' in OT parlance) will work once a source name has been entered. The OT will first try SIMBAD and then, if no result is forthcoming, NED. It is not possible to select which server is queried although the OT will state which one gave the displayed result. In the case of SIMBAD, the OT performs a so-called ``basic query''. The safest method is to enter a non-ambiguous catalogue/survey name such as Cen A, NGC 5128, Arp 153, etc. Catalogue/survey names that include coordinates are okay as well e.g. PKS J1325-4303.
A fairly dangerous kind of resolve criteria is something like J1325-430 (so-called IAU format). This is interpreted as a position around which to search (default radius of 10 arcmin) and will nearly always return the wrong source, unless the positional accuracy is very high. Additional control can result from adding an object identifier to the search e.g. J1325-430=QSO will also return Cen A. A final pitfall concerns the proper motions of bright quasars. The Hipparcos mission measured non-zero values for many of these although, reassuringly, the associated uncertainties mean that the results are consistent with zero. Nonetheless, it is the measured, non-zero, values that will be entered into the OT.
Although an extremely useful tool, given the above issues, resolving source information should be used with care and all details should be checked very carefully. The OT will present a table containing the source information that has been resolved, before this is entered into the Field Setup form. This will warn the user if proper motions or a velocity have not been found and will also give the actual name of the source contained within the database (as opposed to the one that was used for the search). This can be useful for identifying searches that have gone bad. The user has ultimate responsibility to ensure that the source details are correct!