Adding a row of pictures
If you want to add pictures in a row, here are your options:
You can add a Column Divider Widget, and then another Column Divider 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 Column Divider 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 tree in a frame). Separate each image you insert by hitting the spacebar.
Using a gallery
You can also use the Picture Gallery Widget or Flickr Gallery. Please see this tutorial for more details: Photo Galleries.