Set up the microphone in an isolated room, preferably with low ceilings. The idea in using Pro Tools to edit the vocal track is to give it controlled reverb. Rooms with natural reverb (such as a hall or a bathroom) often will sound nice, but it won't allow you to edit that room sound out if you decide it is too strong. A small room with low ceilings will allow you a dry vocal take that you can then edit.
Record the vocal track. To begin recording, you can press the red "Record" button in Pro Tools or press your space bar, which is mapped in Pro Tools as a shortcut to "Record."
Create an auxiliary track by clicking "File," "New Track," "Aux Track" to use for reverb. Select reverb plug-in from your list by clicking "Insert," then choosing the reverb plug-in you like. You may want to try using a few different reverb plug-ins before you settle on one which works best for your taste.
Adjust the level of reverb to a depth you think will work best. It may sound like too much when you listen to the track by itself, but when you put it in the context of the song, you will find that a lot of the excess is lost in the mix.
Mix the vocal track into song by playing it along with any music you have already recorded. You can always adjust the level of reverb as it suits you after hearing it in the song itself.
Set up the microphone in an isolated room, just as in Step 1 of the previous example.
Record vocals by hitting the "Record" button.
Create a new track in Pro Tools, by clicking "File," "New Track," and record a second run of the same vocal part. Try to have the second track match the first as closely possible, including location of breaths and articulation.
Pan the two vocal tracks into separate sides (right and left) of the stereo. Depending on the version of Pro Tools you have (and whether or not you have a physical mixing board attached), the panning option may be located in one of many different locations, so consult your particular version's guide to locate this. If the two vocal tracks are similar enough, you can pan each into its own side of the stereo without having it sound strange or unnatural.
Experiment with the level of panning by starting with both tracks playing through both speakers, then panning each out into their own. There is no "right" way to do this, so try alternate levels of panning until you find one you like. With the two matching vocal tracks running at the same time, it will still sound like one voice but much more full and present in the mix.