On a gamepad, to do a Hadoken, you would "roll" the pad in a quarter motion, from the down position to the forward position, and press punch when you reach the forward position.
To to a Shoryuken, you would move it in a Z motion over the bottom quarter of the pad (from neutral, to forwards, to down, to down/forwards), and press punch.
To do a Senpukyaku, you would do a reversed Hadouken (i.e. a quarter roll away from your opponent) and press Kick instead of punch.
Now, how to do these on the keyboard... I dunno, I've never tried it and I wouldn't want to. I guess for the Hadoken you should try pressing down and then right in quick succession and try to overlap the two. How you would do the Shoryuken confuses me. As you might have guess, the keyboard isn't ideal for fighting games.
When I first played Street Fighter II on the Mega Drive it took me a LONG time to work out how to do the Hadoken and similar moves. I wouldn't be too disheartened that you can't do it right away, just keep practicing. After a while it becomes second nature.