Hi Joanna,
You can achieve this through layout templates (Setup>Interface>Layout Templates). The way you achieve it is slightly different depending on whether or not you are in the New Experience or Classic.
In the New Experience, when you create a layout template you can select the landing page and then add a dashboard (see screen shot below)

In Classic you would choose what page to display on log in via the 'Set Details' tab:

And then add a custom tab to that landing page containing your dashboard via the 'Customize Tabs' Tab:

Once you have created the necessary layout template and assigned it to yourself or your users, they will be presented with your dashboard on their next log in.
Best Regards,
Rich.