Here's the basics of selecting text in Microsoft Word.
Select text by click and drag
Hold down left click over a word on your mouse or mousepad and then drag across the word or words you want to select. Note below how you can drag down/up across rows too:
Select text by double-clicking
Select a paragraph by double clicking on a word with your left mouse button or mousepad:
Select a paragraph by triple clicking on a word in it:
Selecting punctuation
When it comes to punctuation marks like commas and full stops/periods, it's easier to select them depending on where they are in a sentence/paragraph.
Punctuation in the middle of a sentence
If the punctuation mark is in the middle of a sentence, double click just to the left of the punctuation symbol or on it (Note: when selected it will include the space after it). Be careful positioning the cursor before you click as it can get quite finicky in such a small space; too much to the right and you'll select athe word that comes after it instead, take a look:
Punctuation at the end of a sentence
For selecting punctuation at the end of a sentence sometimes it's easier to click and drag over it rather than double click as you have to be very exact. Some finishing punctuation is coupled together when selected e.g. full stops/periods with quotation marks, take a look:
Select a row of text via the margin
Click to the left of a row in the margin space to select the whole row with one click. You can also click and drag in the margin which is a slightly faster and easier way to select multiple rows of text than clicking and dragging over that text.