You should put the roms in the roms directory.
I think the 'N2840' is an 'intel celeron' cpu, running at 2.16 GHz. It looks like this is not a very powerful processor, and if that is true you may not get very good performance from mame at all because of it. There's not much you can do about that besides buying a new and more powerful PC.
The command 'mame64.exe speedup -nothrottle -str 60 -video d3d' should be run exactly like that from a command prompt. It is a kind of benchmark, and in the line that begins with 'Average speed' it will tell you how fast mame can run the game, so you can then compare your results to mine, to get an indication of the relative speed. Also, you can try the command with '-video opengl' and '-video d3d' to see if the one or the other runs faster on your system.
Also, I'm not sure if you are supposed to turn throttle off when running mame normally, because as I understand it, this will make mame run the game as fast as the PC allows, and not at the speed the original hardware did (when that is slower than your PC). You may not notice this if your PC cannot run a game at original hardware speeds (like in your case 'Speed Up', for example), but you will probably notice it when running simpler/older games like 'pacman', for example.