I have found below online courses from Khan Academy very helpful to clear any concepts. Please refer to below links for any topic or go to Khan academy website.
Trigonometry with right triangles
Learn the basics of trigonometry: What are sine, cosine, and tangent? How can we use them to solve for unknown sides and angles in right triangles?
Trigonometry with general triangles
Learn how to use trigonometry in order to find missing sides and angles in any triangle.
The unit circle definition of sine, cosine, and tangent
Learn how the trigonometric ratios are extended to all real numbers using algebra. Start solving simple problems that involve this new definition of the trigonometric functions.
Graphs of trigonometric functions
Learn how to graph trigonometric functions and how to interpret those graphs. Learn how to construct trigonometric functions from their graphs or other features.
Trigonometric equations and identities
Learn how to solve trigonometric equations and how to use trigonometric identities to solve various problems.