Select a row

Click on the row heading.

Select several adjacent rows

Drag across row headings. While you are dragging, a popup tip shows how many rows are being selected.
Excel 2007, 2010:
Excel 2013, 2016:

Or click on first row heading you want to select, hold SHIFT down and click on last row heading that you want to select. All rows between are selected.

Hide a row

Set Row Height = 0

Or drag bottom edge of row heading up until the row is hidden.

Or right click on selected row or rows and choose Hide 

Unhide a row

Drag from a row above to a row below the hidden row. Right click on the selection and choose  Unhide  or set row height to something besides 0.