When you have three or more cards that can form a meld, make sure they are arranged together in your hand. Depending on your Settings, the game will usually arrange your cards automatically into a meld. However, you are also free to drag your cards manually. When arranging cards of the same suit into a Run, note that the cards must be arranged left-to-right in ascending order. 

When cards are successfully arranged into a meld, there will be a visual representation in the form of a colored bar along the bottom of the cards. When you can play the meld, an arrow button also becomes visible.