Okay... first of all, this is probably the first difficult challenge to anybody running a 3d printer for the first time. That's the bad news. The good news is that once you find the sweet spot for the bed level, you can probably enjoy 3d printing a lot more. (There are other challenges, but bed leveling is one of the first and could very well be the most challenging.)
The bed has been machined at the factory to be flat and it most probably is flat. So we can probably forget worrying about that. For this topic, we assume the bed is flat.
The Simple Left vs Right Level adjustment:
When you sense that your bed is lower on the left compared to the right... you are faced with the simplest of bed leveling problems. We can easily cure this and make the bed level by simply turning the left z-thread rod ever so slightly to bring down the nozzle on the left side.
Important: Turn off Trinus before trying to turn one or both z axis leadscrews; they will probably refuse to turn if the power is on.
How much do you need to turn? Very little really. If you look at the z lead screw, you can see the large threads; the distance between two hills is what we call thread pitch. One turn of the lead screw will cause that side of the x axis mechanism to go up or down equivalent to the thread's pitch. So you really only need to turn the lead screw very little (10 degress turn means 10/360 = 0.02 = 2% of the pitch length). This procedure actually gives you a very detailed level of adjustment for left and right heights.
Edit: Someone asked whether it is better to loosen the screws that attach the x-axis actuators to the two z-axis actuators (left and right). For very small manual turns of a z-axis (of a turned off Trinus), you can get away without loosening the screws between the x-axis and y-axis. Small manual turn means 10-20 degrees clockwise or counter-clockwise. If you end up turning a leadscrew more than 20 degrees, it would be better for you to loosen the screws that attach the x-axis to the y-axis.
Suggestion: Always take a memo of what you are doing at each step of leveling... which you turned, clockwise or counter clockwise, how many degrees, how much did the distance between the nozzle and bed change... The reason for this data collection is we easily forget what we did, and when we find we over-turned or turned in the wrong direction, you have no way of getting back to the state where it was before you manually tweaked one of the z-axis.
The Difficult Front vs Back Level Adjustment:
When you sense that your bed is lower in front than in the back... you are faced with a more difficult chore. Difficult because there is no easy manual screw to turn. You will need to unscrew the Y-axis actuator and insert a shim (piece of paper or piece of aluminum foil) where it is lower (front or bottom). This is a trial and error process, but you can probably make a good estimate of how many sheets you need as shim to get a relatively level bed (front relative to the back). You can also chime in with other users to learn what sort of shim and how many sheets they needed in their case... but note that this is a case-by-case issue so treat other people's details to the problem only as rough reference.
By the way... take it easy in tightening those steel screws against the aluminum threaded hole. Too tight can cause the thread in the aluminum hole to get stripped and permanently damaged. A slightly loose screw is a lot better than an impossible to tighten screw due to a damaged threaded hole.
The Really Difficult One Corner of the Bed Level Adjustment.
Now, this is the most difficult to do... difficult only because in most probability, you can't get it level in just one try because we have two variables that we need to tweak together... the left-right, and the front-back. And where to turn (left or right) and where put the shim (front or back) is not intuitive. You can only do this by trial and error and probably several trial/error attempts are needed before you can say... okay... that's the best I can do... now to start printing something really nice.
When you have to tweak both the left/right and front/back leveling, it is usually better to treat the corner as separate operations... do the left/right first, and when you get that right, then do the front/back (which is harder to do actually).
More information can be found on our Forum: