Maths Teacher, can teach student till University level

I have taught 9th 10th & 11th Grade maths for almost 2 years in corona times to a batch of 20 students.
Now, I am in Germany doing my Masters, and I in my free time I love teaching Maths to a German University student and another high school student.
My main focus is to help the student learn the fundamentals of maths, which plays a major role in learning concepts at every stage of learning.
Many students say that they can't understand maths, So, I am here to fill that gap.
In My Experience of learning & teaching, I found that Learning maths is not through reading and remembering the formulas but rather understand the underlying concepts and applying it to problems, making mistakes and learning from those mistakes.