I have the following sentence:
When I press Tab on the second line, the top line indents as:
I want the first line to stay where it is at and just indent the second line. How can this be done? I am using Word 2013.
The quickest solution I can think of is to go to View, then check the Ruler.
Alternatively, between the toolbar and the Layout, on the right, a button that looks like the following should appear:
Assuming you are in the Print Layout, two rulers, one on the top and one at the left, should appear. On the top Ruler, you can see some indentation marks (e.g. in your case, they look somewhat like an hourglass).
From top to bottom, they are:
Move the 2nd mark (hanging indent, e.g. the triangle pointing upwards) to the start of the margin, as shown by the shaded area of the ruler. This will make so that only the first line is indented.
You can also edit the Paragraph settings such that only the first line is indented. You can access them as the following picture shows or by right-clicking on the actual paragraph and accessing the dialog from there:
A practical demonstration of the problem and solution.
All screenshots are done on a Portuguese Word 2007. Essentially, after activating the ruler, you can move the 2nd mark so that it matches the margin. The text follows suit.
If you used the Paragraph dialog, you would need to set up the paragraph in a way similar to what I show. In particular, the Left Indentation should be 0 and the Special Indentation (first red box on the Paragraph dialog) should be set up as so it reads First Line and afterwards how much indentation you want.
A good thing about the dialog is that it allows a preview in the bottom, so that one can see approximately what changes are being made before closing it.
Just hold down the Ctrl key when you press Tab at the start of the first line: this causes Word to insert a Tab character, rather than indenting the whole paragraph.
Note: this won't use a style to apply the first line indentation, so isn't recommended if you're working with a large or complex document which may need universal edits. But it is the most simple solution, and just fine for small documents.