How can I select multiple jobs on the jobs tab at once?

To select multiple jobs you can either:

Check the box at the far left or each job line that you wish to select

Or you can highlight all the jobs in view using the checkbox at the far left of the blue tool bar above any lists of data, next to the column title "Due"

Once you have selected the jobs you require you can perform whatever task you need to - eg) Send SMS/Send email etc