How can I add text in my theme?
By Default Drupal front page shows the list of Contents you create, the number of contents you can list is controlled in Site Configuration. To answer you particular scenario would be too much of an answer here, I'd recommend you to read some Beginner Documents or watch some Videos in the net. Good place to Start is Drupal documentation

To displaying content in front page go-to UR-URL/admin/config/system/site-information and change the default front page to node/1 (in your case). This will display static front-page when your created the Basic page. 

Be aware this is not the best bet, so, I'd suggest you to explore Drupal bit more before actually starting the site building.