It’s possible that a model will be oriented incorrectly after import. This happens especially when the model was exported from a 3D modeling software that uses a different axis orientation. The fastest way to rotate the model into correct orientations is with the Place on Face tool F.
First, select a model you wish to re-orient. Then press the F key or pick the Place on Face tool from the left toolbar. Multiple white planes will appear on the model. Clicking on any of the white planes will align that plane with the print bed.