The purpose of the Baseline is to highlight in the gantt chart a specified date that serve as a reference for the complete planning.
This date is not necessary the actual today’s date: if your presentation is in 2 weeks, you may consider to already set the baseline to a future date and see how the chart will look like.
The baseline is useful to highlight the tasks that are behind schedule and the ones that are progressing according to plan. Basically, any task behind the red line which is not 100% completed is in delay.
If you would like to change this date, select from the left panel an appropriate date:
You can also use the ribbon menu :
Once done, the Gantt Chart will update automatically the red bookmark and also check one more the due dates of all the tasks against this line.
If you would like to completely hide this line from your gantt chart, just set it to a date in the far future (e.g: 01/01/2020).