Principal Solution – The least value of unknown angle which satisfies the given equation, is called a principal solution of trigonometric equation.
General Solution – We know that, trigonometric function are periodic and solution of trigonometric equations can be generalised with the help of the periodicity of the trigonometric functions. The solution consisting of all possible solutions of a trigonometric equation is called its general solution.
Here are the NCERT Solutions for this chapter where you will find many question on these topics. You can refer these to understand how to find the values.
You can also refer to this video which gives few good example to find these values