There are multiple ways.
1: There are several apps on splunkbase, including Welcome Page Creator.
2: You can create your own app with Apps -> Manage apps -> New -> barebones, Go to that app, create a default dashboard, then go to Your Login Name -> Account Settings -> Default application and change it to your new app.
3: Click the Splunk icon/name in the upper right which will take you to your default app which will be Search & Reporting if you have never changed anything. Notice the big gray area in the middle that says Choose a home dashboard. Click on it!
