Take off the trim from the perimeter of the floor with a pry bar and hammer. Keep the trim intact as you remove it.
Lay a course of plastic underlayment on the floor along the starting side.
Lay a Swiftlock floorboard at one end of the floor, in the corner. Put spacers between the board and the two walls.
Lock a second board off the end of the first, snapping them together by pressing the end of the second board over the end of the first, so the tongue-and-groove fitting snaps into place.
Lay the rest of the first course end to end, along the whole edge of the floor. Cut the last board on a miter saw to fit at the end.
Lay the second course of Swiftlock boards alongside the first. Connect them by setting the boards of the second course at a downward angle against the edges of the boards of the first course until you hear them click into place.
Proceed across the floor course by course, arranging the boards of each course so the ends aren’t lined up with the boards of the previous course. Work your way across the entire floor.
Cut the boards for the final course on a table saw, along their lengths, to fit alongside the ending wall. Cut them to leave a half-inch gap between the final course and the wall.
Reinstall the floor trim, using a trim nailer. The trim will cover the spaces around the perimeter of the floor.