I had no problems as I installed the mainboard:

The graphics card comes next. To install an expansion card you have to remove the protective panel:

Expansions cards are fastened with screws, which is good. Screwless latches are handy, but are not as reliable as screws. So, the card is installed:

The hard disk drive goes into its place then:

Just insert it into the cage and fasten with four screws. It’s somewhat more difficult with the optical drive. There is no clear marking on the cage as to the position the drive is to be fastened at. So, you should fasten it first in such a way as to leave it some freedom to move along the rails:

Then you put the cage into the case, press the drive against the front panel and see which mounting hole to use:

Then remove the cage, fasten the drive and mount the HDD cage:

If you don’t have a second HDD, you can use the free room in the cage to tuck away the interface cables. You shouldn’t yet put the 5.25” cage back in its place so that it didn’t get in your way during the rest of the assembly process.