Things like that are going to be entirely down to the University's individual policy on degree progression... and it will probably vary within University deparments and may well vary degree by degree.
From my own experience of Aeronautical Engineering at Glasgow:
1) If you fail a module, there is a resit in August. If you fail the resit, you may be allowed to retake the module again the following year in parallel with your new subjects without failing the whole year, but depending on the importance of the subject and how many modules you fail, you may be stopped from progressing to the next year until you pass those modules.
2) We didn't have any graded labs. We did labs, and sometimes we had to write lab reports based on those labs which contributed towards your final mark in the module. In some modules it was not necessary to complete this to pass the module, and in other modules it was.
3) Labs vary by subject. In labs for thermodynamics and propulsion we ran experiments with propeller engines and jet engines in the wind tunnels. In aerodynamics we did experiments with wings in the wind tunnels, as well as other fluid experiments. In design labs we designed and built prototypes of our designs. In dynamics/statics/structures labs we analysed and conducted experiments with dynamical systems, structures, aircraft components, etc. In electronics labs we built and tested analogue and digital electrical circuits, as well as designing them using circuit board design software. In MATLAB labs, we learned how to model systems in MATLAB. In CFD labs we learned how to use fluid dynamics modelling software packages like Numeca.
But, really, all of this information is useless to you unless you're doing the same specific degree course at the same university. And even then, I gather that things will probably have changed at Glasgow since I graduated (in fact, I'm sure they have).