BMW Torque Teightening Specifications are used for tightening various different nuts, bolts, screws etc. to the correct strength. Over tightening parts can cause a lot of trouble, i.e. stripped heads, damaged nuts, threads, etc.
To tighten to a correct specification, you will need to acquire a Torque Wrench, instead of the commonly used Socket Wrench. A Torque Wrench allows you to manually set the level of tightening and then once it has reached that tightening (whilst using it), it will stop applying any more pressure and will make a click-click sound.
Torque Wrenches are available in different sizes i.e. 1/4, 1/2, 3/8, 3/4. In turn, each size is capable of different levels of Torque e.g. Torque range 20-150lb/ft. 28-210Nm. When buying one, most importantly check the Torque Range. A similar one as shown below can be bought for £15 from Screwfix.
The below photos show what one looks like, also a close up of the Torque settings control.