trigonometry periodic functions from circles

[Chuquis]

Can someone please explain to me how I can find sin, cos and tan from a unit circle?

[Crimson Sunbird]

Starting at the point [latex](1,0)[/latex] on the circle [latex]x^2+y^2=1[/latex], move the point anticlockwise along the circle through angle [latex]\theta[/latex] to the point P, where [latex]\theta[/latex] is in radians and [latex]0\leqslant\theta<2\pi[/latex]. The x-coordinate and the y-coordinate of the point P are [latex]\cos\theta[/latex] and [latex]\sin\theta[/latex] respectively, and [latex]\tan\theta=\frac{\sin\theta}{\cos\theta}[/latex].