Bolt open:

To load a magazine fed rifle, the bolt handle is lifted up and pulled right back, on modern rifles this cocks the firing pin mechanism which is contained in the bolt, and a loaded magazine inserted. The magazine is designed so that the top catridge sits in such a position that the closing bolt catches the top edge of the cartridge rim and pushes it forward. Magazines vary in their design. They can all be loaded out of the rifle but some magazines can be left in and loaded by inserting individual cartridges through the loading port and pushing them down into the magazine until it is full.

Bolt closing:

As the bolt reaches the end of it's travel, the bolt handle is pushed down to lock the breech. At the end of the bolt, there are solid metal lugs. As the handle is closed, these lugs slide into grooves in the receiver and lock the bolt in position. A solid lock up is critical because, as the rifle is fired, it is the bolt that withstands the equal and opposite reaction that would otherwise propel the bolt out of the back of the rifle with similar energy to the bullet going forwards!

Ejection:

Once the shot is taken, the bolt handle is lifted and pulled backwards. On the bolt face there is a rim that encloses the end of the cartridge. Part of this rim, the extraction claw, is sprung so that as the bolt is closed, it clips over the end of the cartridge. On the face of the bolt is a firmly sprung metal button that is forced to retract into the boltface by the cartridge as the bolt closes. When the bolt is withdrawn, the extractor claw pull the empty case out of the breech. When the case reaches the loading port opening, the sprung button flings the case out of the rifle.