You can get Salesforce1 in different ways:

As a downloadable app from the App Store and Google Play™. Users can install it directly on iOS and Android mobile devices.
As a mobile browser app that runs in supported mobile browsers on Android, iOS, BlackBerry, and Windows 8.1 mobile devices. This option doesn’t require anything to be installed.

(1) Enter your username provided to you at the start of the trial. It will be in the form of an email address.
(2) Enter the password provided.

Your screen may vary depending on your company setup, but the navigation will be the same across all configurations.

(1) Main menu bar. Click the 3 lines to open a menu showing all screens and objects you can view. In the screen above, the Account tab is being shown.
(2) Search bar. Within this bar, you can search for whatever tab you are currently showing. In the example, you can search all accounts.
(3) Detail link. Click on any link in the main screen to display the detail record.

After clicking on the three lines at the top, you are presented with a scrollable menu of all options. In this example above, you can quickly navigate and see the Part Research screen, Reports, and Dashboards along with other options.

Clicking on any of these options will take you to that screen.