Ok, so you've most likely come here to learn to play the second least used job in Barotrauma. Good. Then lets start:

So first off: I am gonna break this tutorial down into three parts:
-Characteristics, where I will talk about the basic stuff thats the Mechanic the Mechanic.
-RECOMMENDED Gear/Equipment: Essentially just me posting in a picture of my usual/recommended inventory and talking about it.
-WHAT to do WHEN and HOW: What the name says. Also, some stuff about routines.

Number 1: Characteristics

The Mechanic, also sometimes just called Mech (despite him not being a robot) can be considered a worker class (which merely are him, and the Engineer)
Therefore, his job is obvious: Fixing the hull and certain machinery, great.

For that, he has the highest construction skill, which allows him to safely wield tools and create ALL given items in the fabricator.
On the latter, he is the ONLY one capable of fabricating nuclear shells and Incendium grenades, both extremely destructive weaponry which he normally wouldnt even have clearance to use (Life sucks). He is al´so mostly the only one able to make tools, which can be very useful on ships with decent materials for cargo, yet scarce tools.
But lets look into the other advantage of a high construction skill, the tools.
Mostly, the Mechanic is the only one capable of using a cutter safely and efficiently. (Since it requires a skill of 30, while the welder has one of 20.)
That makes him essential to ruin salvage missions.

But anyway, lets rather talk about what "safely" and "efficiently" means here, since its a lil interesting.

Safely: Well, thats easy to explain,if you use a welder or cutter as someone with low construction skill: You can damage yourself. Just hover the flame over your body and you will lose health, which a "trained" personnel will not (Because it makes sense for assistants, captains, etc to not know that you are not supposed to be holding the flame on your knee).

Efficiently: So thats a lil more interesting, and most of you probadly didnt even notice it (I didnt either, until I looked at the .xml files): If you are untrained, you deplete fuel/oxygen thrice (3x) as fast as a trained personnel would, which can change things, alot. Especially on ruin missions, as said previously.

Also, people claim that Mechs can fix walls faster than others with a welder, which seems to be true, tho, not by a lot.
On a ordinary wall, a captain with Construction wkill of 26 needed ~3 seconds to fix it shut and ~ 9 seocnds to break it down with a cutter.
The mech with a skill of over 50 needed ~2.5 seconds and ~6.75 seconds to break it down with a cutter.
can't however be sure if that matters too much, maybe at the cutting speed.

Also, the THIRD aspect (Yes, there is a third) of construction skills is fixing machinery. Those include:
-Doors (Important, like really, if a creepy crawler makes it to your airlock doors, you are doomed without a mechanic to the rescue)
-Engine (Also important, for obvious reasons. Breaks pretty often in floods.)
-Reactor (Yea, important, power, etc.)

Number 2: Starting gear

-Basic Equipment
-Welder with Fuel Tank inside
-Cutter with Oxygen Tank
-Fire Extinguisher
-Diving Mask with Oxygen Tank Inside
-Spare Oxygen Tank

Yea, basically, this is the loadout I prefer with him. Spawning stuff, Tools, Masks (Both filled with oxygen/fuel), a spare tank, and a fire extinguisher. Of course, not everything has to be there, and sometimes you would rather have your medicine with you rather than a fire extinguisher.



Number 3: The Action: Now to your actual work/routines: I am just going to list them here, since most has already been said:
-Check the reactor freqeuntly
-Check the status monitor for possible breaches
-Fix walls of a previous breach to maximum
-Check sonars for possible creatures and man guns if there are any approaching
-Visit the doctors if injured
-Possibly help Security to catch the clown.
-After a breach, check the engine
-Fix every broken door, unless it leads to the command and the captain is either unwilling to drive, lost, or AFK

Well, that has been the semi-informative tutorial on the Mechanic, I hope that you will be able to atleast partly utilize the given tips and *maybe* survive make the sub survive a little longer from now on.
- Frost