You can use your charging cable to plug it via USB. The iTunes icon looks like a blue-and-pink musical note in a white circle. You can find it in your Applications folder on a Mac, or on your Start menu on Windows. If this is the first time you're plugging your iPhone into this computer, tap Trust on your phone's screen to authorize the connection. This button is located below the Play button in the upper-left corner of iTunes. It will open your iPhone's navigation panel on the left-hand side. If the phone icon opens up to any other tab than Summary, click the Summary tab at the top of the left panel. This tab will display your phone's hardware, storage, and backup information. In the Summary tab, find the Backups section, and make sure This computer is selected under the "Automatically Back Up" heading. Under the "Manually Back Up and Restore" heading, click this button to back up your data to your computer. All of your text messages will be backed up, along with your documents and settings.
Plug your iPhone into your computer. Open iTunes on your computer. Click the phone icon on iTunes. Select This computer under the Backups section. Click the Back Up Now button.