Drop an image onto the window, or click the frame in the center of the screen to choose one. Drag the text to move it and resize it with the corner and edge handles. The panel names at the top right open and close the Main, Layer, and Text panels.
In the Text panel, choose Font, Layout, or Color and Effect, and those values appear in the child panel beside it. Panels can be dragged by their header, and double-clicking the title pins them to the top right. Save your finished meme as a PNG from the Main panel.