Woodnthings gives a nice description of glulam and microlam (or laminated veneer lumber--LVL) beams.
A glulam beam will be much stronger and stiffer than the same pieces of wood just stacked on top of each other. For this to work, the gluelines must be rigid so the wood pieces can't slide past each other, even minutely and slowly, under load. In industry this is always done with glue intended for structural applications, not just any glue. The PVA or aliphatic resin glues that carpenters and cabinet shops use will not resist long term stress without slippage. They are not intended for structural applications. Industrial laminated beams use phenolic resins--possibly some urea formaldehyde resins outside the US--which cure to rigid gluelines which withstand shear stress indefinitely without slippage. Resorcinol glue is the best substitute outside a factory. There are caulk type construction adhesives that would be second best, especially if clamping pressure is applied with wood screws.
A microlam beam is entirely different. If you glue several wood pieces together side by side, there is no shear stress on the glue lines between them when the composite beam is loaded. The beam deflection calculation (the bending moment) for the composite beam is the simple sum of the calculations using the bending moments of the individual beams. The individual beams will bend in unison with out without the glue. There are some buckling considerations when the plys are very thin compared to the beam depth, and gluing it all together will make it easier to work with.
A microlam type beam made of OSB or plywood will not be as strong or stiff as a properly glued glulam beam made of solid wood and the same size because the OSB or plywood is not as strong or stiff as solid wood as the long grain structure of the wood has been disrupted in those board products. True microlam beams have the grain in all the individual plies aligned, not criss crossed as in plywood.
I did a lot of beam deflection calculations when I worked in the window industry. Window mullion calculations are simple because they just consider short duration wind load rather than combinations of short term and long term live and dead loads. There are some odd combinations of distributed loads and concentrated loads in mullion configurations put together for aesthetics.
For a small project like yours there are handbooks of standard wood frame construction. In the US they are in imperial units, but you should be able to find metric versions.