Climbing knots have different purposes: for tying the ropes (including different thicknesses), for fixing the climbing harness, for stationary fastening of the rope, as a device for lowering / lifting for lack of other means, etc.
Bowline
Serves mainly for fixing the harness. The end of the rope is passed through all the loops of the harness (upper and lower), then a knot is knitted. It can also be used to create an impromptu harness from the end of the rope in an emergency: the free end is wrapped around the chest and a bow tie is tied (similarly, water-tourists work when it is urgent to pull a person out of the river). In some cases, other climbing nodes can be used to fix the harness, for example, a straight one with control knots. The bowline also serves to fasten the railing with a loop around a stone or wood without using a carabiner.
Eight
It is a more reliable analogue of the node-conductor. The same conductor, only with an additional revolution. With the help of a figure-eight and a carbine, the climber is fastened to the safety rope; stationary railings are attached to a hook or ice drill by a figure eight through a carbine.
For tying ropes of equal thickness (for example, when there is a need to build a rope), straight and grapevine climbing nodes are used. The latter is more reliable (a direct knot must be fixed with control knots), but has a significant drawback: when it is delayed, it is almost impossible to untie it. In some cases, you can build a rope by connecting two conductors with a carabiner.
Prusik (gripping knot)
Designed for ascent / descent along fixed rails. The classic way. At present, other climbing equipment is used for these purposes: for climbing - zhumaras, for descent - eights, petals, etc. This is more convenient than a knot. A Prusik is also used as a clamp for a taut rope when working with a chain hoist (a system by which a group pulls a victim out of a crack, pulls a rigid ferry across the river, etc.).
"Hare ears"
Used for insurance requiring increased reliability. For example, to raise an incompetent participant with an accompanying person from a crack.
There are climbing nodes for tying ropes of different thicknesses, the main rope and the cord: oncoming, brahmkotovy. In real life, they are rarely used.
Stirrup
It is used, for example, when climbing a fixed rope. The loop with a stirrup for the foot is attached to the jumar, the second jumar is fastened to the chest harness. The jumar with a loop extends up the rope, the climber rises on a stirrup and moves the chest jumar to the foot. Stirrups are used to lift the victim, if he is able to move himself, and in a number of cases.
All of these nodes are mountaineering, but some of them were invented before, then they were considered marine. And now they are used not only in mountaineering or industrial mountaineering, but also in other types of extreme activities: water and speleotourism, rescue work and any situations where the use of a safety rope is required.