The size of most traditional geometry frames is described by the length of the seat tube as measured from the center of the bottom bracket (pedal crank) shell to either the centerline of the top tube or the top of the seat tube (where the seat post slides into the frame). As a rough estimate, at 5' 7" you should ride a frame with a 52 cm - 56 cm seat tube (center of bottom bracket shell to top of seat tube), depending on your leg inseam measured from the floor to snugly nestled in your crotch in stocking feet. See the attached road bike size chart.
For safety reasons, you should be able to straddle the bike's top tube with some clearance between the top tube and your crotch. This is called standover height.
Lugs are reinforcements used to join the tubes of a frame, and are typically brazed to the joined tubes. For examples,
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