What can laughing gas make people do and does it help with surgery?

Nitrous oxide. Is an inhaled anesthetic that has some analgesic and anxiolytic properties. In a general anesthetic it can be used as part of a balanced technique, but can cause bowel distension and, in high concentrations, post operative nausea.
It helps..yes. Nitrous will help the patient decrease their anxiety and relax which will help allow for the anesthetic to work better during surgery. However if the pateint is already relax, there is no need for it.
Depends. As with any medication or drug, patients respond and react in different ways. Nitrous oxide or laughing gas affects patients in different ways. I tell my patients that one group may feel lightheaded and feel like they are floating, another group may feel very heavy, and some may feel no different than before. For most patients, nitrous does relieve some anxiety and a more comfortable visit.