Hello! If you press 'P' to open the pause menu, you can choose between the grappling hook and the sticky jumper (the sticky jumper is the default option). Then, you can left click and hold while pointing at a part of the terrain to use it. The reticle will turn green when you are aiming at a valid target within range.
As for the camera, it sounds like your mouse isn't captured by the itch.io game window. Try pressing 'P' to open the pause menu and then 'P' again to close it, and it should fix the issue that you're describing. Then, you can look around freely with the camera.