On the other hand, a luer slip connector (on the right) does not have a screw-like feature. Instead, it relies on a friction fit to attach the male and female parts of the connector together. The male end of the connector simply slides into the female end, and the two parts are held together by friction.
Once connected, the way they work is simple. Fluids (either medicine or blood) are drawn up through the needle into the syringe, by pulling back the connected syringe plunger. Keeping the needle tip in the fluid source while the plunger is being pulled, ensures no air enters the syringe.
To dispense fluid from the syringe, through the needle tip, the same is repeated in reverse. Once the fluid has been drawn into the syringe, the needle can be inserted into the patient, and the fluids dispensed. If you are taking blood from the patient, then this will be dispensed where desired (depending on the use case).