Adding a row of pictures
If you want to add pictures in a row, here are your options:
You can add a Columns widget, and then another Columns widget inside one of the columns (then you'll have four columns). Then, add a Picture widget into each column - you can add as many Columns widgets as you like, bearing in mind that you might be restricted by the width of your chosen style.
Using a Text widget
You can use a Text widget and then click on the "Picture" button on the Text Editing Toolbar (the icon is a picture of a mountain). Separate each image you insert by hitting the spacebar.
Using a gallery
You can also use the Gallery widget to showcase your pictures. Please see Using the Gallery widget for more information.