I've seen this set up a few different ways. You can use the tab key several times, or, even worse, just use the space bar, to line up the text. However, the better practice is to set the left indent. I've drawn an arrow to identify the left indent in the picture below:
Drag the bottom rectangle to the spot on the ruler where you want the text of your line to start. Here, I wanted everything to be indented 3.5", so I just moved the ruler over to the 3.5" mark, and every line started there.
Why is this better? Well, in order to create the same layout using the tab key, you would end up having to hit the tab key 28 times:
And it is hard to tell how many times you would have to hit the space bar to get everything to line up right. It is much simpler to adjust the left indent once than it is to constantly hit the tab key.
Second, by using the left indent you can line things up in the exact location you want. Let's say you want something to be indented 3.35". You can easily set that with the left indent, but hitting the tab key will not ordinarily line you up at 3.35". The left indent gives you finer control.
Last, though certainly no less important, when you use the left indent, it is much easier to edit later. Let's assume you want to add the name of your firm below your name, but it is so long that it won't fit on one line if you have everything indented at 3.5". With the tab method, you will have to go through and delete tabs on every line. With the indent method, you simply highlight the lines that need changed and readjust the left indent slider.
In short, if you find yourself hitting the tab key more than once when formatting a document, be it for signatures, block quotes, or any other reason, you should stop and ask yourself whether you should really be setting the left indent instead.