Hi Elaine!
In general the tick mark labels and locations are controlled using the Axis settings.
If you are plotting a date axis, the labels are set automatically depending on the size of the graph and the range being plotted.
For example, here is a graph where we have set the size, and every other month is labeled.
Click and drag across the screen to zoom in on a section.
Now, there is more room, so every month is labeled.
If you want to have more exact control, you can make columns for where you want the date placed and the label to go along with that date.
Then change the axis settings for X tick marks from ‘Automatic’ to ‘Labels’.
Select the columns for the location and labels, as shown.
Hopefully, most of the time the automatic settings will work for you for dates. If you think the automatic settings are not giving you the best result, please send that example along.
Hope this helps!