Is there any good textbook for theoretical economics mathematical modelling? I am currently reading some theoretical economics books and, of course, many mathematical expressions appear. I kind of guess their meaning, but it takes a lot of time and, after all, my guesses are assumptions rather than certainties. Many times I find myself lost even in the easiest questions like: why use an exponent instead of a multiplication in this particular case? And even if I kind of guess their meaning, I struggle to understand the creation process of a model. I have looked for mathematical modelling textbooks but all I kind find are introductions to models for processing big data or data analysis. I would like to read a textbook that is fully focused on theoretical models. Also, the books I find for mathematical economics and such are books that teach how to solve specific problems rather than how to formulate models. Does anyone know any good textbook for someone like me? Thank you.
Your question seems a bit broad. What kind of “theoretical economics” are your reading?

Nevertheless, I infer from what you write that you need to start from the beginning with maths for economcis (and maths in general), (this is because of your comment not knowing when to use an exponent  and when to multiply.

Having said this, I would recommend:

“Essential Mathematics for Economic Analysis” by Hammond et al

This book starts at the basics and builds up mathematical tools to study economic ideas.

Having mastered this book, I would try

“The Structure of Economics” of Eugene Silberberg. This books is more advanced, but it is “economics with mathematics”, so having aquired the basic mathematical tools in the first book, this book focuses con economic models from a mathematical standpoint.