The simplest way is likely this. No sin and cos even needed (although DBPro does it internally).
inc cax#,mousemovey()*0.2
inc cay#,mousemovex()*0.2
rotate camera cax#,cay#,0
rotate object objnum,0,cay#,0
if upkey() then move object objnum,10
if downkey() then move object objnum,-10
if rightkey() then turn object right objnum,90 : move object objnum,10 : turn object left objnum,90
if leftkey() then turn object left objnum,90 : move object objnum,10 : turn object right objnum,90
Of course there are better ways, but this is easy to understand and good for starters.
