I don't have the energy to go into it in too much detail today.. Firstly, check the spec of your onboard sound chip. It may already have a DAC. In which case you can get some amazing amps for £70. The DAC is not the amp. It is a digital to analogue converter, which you may or may not like. It is popular with any one over the age of about 30, because they were raised on analogue sound.
The important part is the amp. Now with home audio speakers you ideally want an amp that can output, in RMS, (so continual) around twice to 2/3 more than your speakers are rated at. This may sound crazy, but it is the only true way to avoid any clipping. Clipping = pops, farts, distortion etc. These can all blow up a speaker, even if it is rated for 1000w and the amp can only push 250 for example.
And for me when I made the transition into headphones and Head-fi I like to use the same principle. That way the amp doesn't even get warm, nor distort or clip. It's always better to have too much power on tap, that way you can extract every last bit of performance from your headphones. It only takes around 9 O'clock on my Beyer clone for example to get my Grados singing to their full capacity. Meaning everything runs cool with no distortion and so on.
So yeah, first see if you need a DAC. Then read about it and decide if you even want a DAC, then make your choice.