To lean something against (a wall or other support); to set or prop something up.
使わない自転車を門の横に立て掛けておいた。
I leaned the unused bicycle against the gate.
絵の額を壁に立て掛けて飾った。
I propped the framed picture against the wall to display it.
梯子を窓枠に立て掛けて屋根に上がった。
I leaned a ladder against the window frame and climbed onto the roof.