The sonic screw driver first appeared in the 1968 episode, fury from the deep where the doctor used it to escape from a prison by picking a lock with it and ever since then the sonic screwdriver has saved the doctor and his companion many times. When the sonic screwdriver first appeared it was only able to pick locks and over time it has gained many more abilities.
The sonic screwdriver is able to hack into computers which helps the doctor obtain information. It is also able to defend against some types of assault weapons by frying their internal mechanics and causing the weapons to burst into flames which helps the doctor escape from some dangerous situations. It also has the ability to electrify the nervous system to stun his enemies and escape.
Throughout the many seasons of Doctor Who the sonic screwdriver has gotten the Doctor and his companions out of sticky situation and has help them obtain important information and without the sonic screwdriver the doctor and his companion wouldn’t be able to do a lot of the things that he does.