how do I align the text so that each sentence starts in the same place?

Your left indent and your tab settings need to be the same. If the number pushes the text beyond the tab setting, the text will move over to the next 0.5 inch measurement (if using inches).

Since you may have to account for double digits (beyond 9), you should move the left and tab setting to the right in your paragraph style.

Create a hanging indent. For example, set the left-indent of the paragraphs to 1 inch (if that is enough to account for the long subsection number), and set the first-line indent of each paragraph to -1 inch.

Then, make sure to separate each subsection number and the text that follows it with a tab rather than a simple space.

All the subsections will now be aligned left, and all the text will be aligned on the 1-inch mark.