(1) To be able to relax; to be comfortable and at ease. (2) (In some contexts) to make someone else feel relaxed.
この部屋は広くて家具も少ないので、よくくつろげる。
This room is spacious and has few pieces of furniture, so it's easy to relax here.
彼女の笑顔を見ると、周りの人も自然とくつろげる。
Seeing her smile makes the people around her naturally relax.
新しいソファは座り心地がよくて長時間くつろげる。
The new sofa is comfortable to sit on and you can relax on it for a long time.