I have trouble to reading this book!
What book is more elementary/preliminary than this book: Introduction to Stochastic Processes by Lawler
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It is very difficult to answer your question with the information given.
These might be more gentle and the last one uses Maple.
$\bullet$ Introduction to Stochastic Processes, Paul Gerhard Hoel, Sidney C. Port, Charles J. Stone
$\bullet$ Adventures in Stochastic Processes, Sidney I. Resnick
$\bullet$ An Introduction to Stochastic Processes and Their Applications, Petar Todorovic
$\bullet$ An Introduction to Stochastic Processes, Edward P. C. Kao
$\bullet$ Informal Introduction to Stochastic Processes with Maple, Jan Vrbik, Paul Vrbik
Maybe if you can describe what issues you are having, we could provide more guidance.
There are also some older books that are excellent, but I am not at home and the titles are escaping me.
Look through the entry for Stochastic process in Wikipedia. You'll find some references and suggestions for further reading.
Another possibility is to go to a university library, search for "stochastic processes", and sit down to browse through the books available, to see which among them suit your needs. Bring the text you refer to with you, and compare how various texts differ in their coverage and explanations that you find too difficult to comprehend as given in your current text.
You might want to download the text (available in pdf from Prof. Oliver Knill at Harvard) on "Probability and Stochastic Processes with Applications.". You can compare the text with yours, with no cost to you!
One additional possibility to consider, which you can preview, is Introduction to Stochastic Processes, by Hoel, Port, and Stone. Peruse the table of contents, and sample the writing to help you determine if you think this might suit your needs.
Applied Stochastic Processes in science and engineering by Matt Scott from the University of Waterloo is free online. It emphasizes ideas and methods.
Stochastic processes by Sheldon Ross is very elementary:
A nonmeasure theoretic introduction to stochastic processes. Considers its diverse range of applications and provides readers with probabilistic intuition and insight in thinking about problems.
Maybe the easiest one to read (I wrote it myself so my point of view is biased) is the following: "Applied Stochastic Processes, Chaos Modeling, and Probabilistic Properties of Numeration Systems." Published June 2, 2018. Author: Vincent Granville, PhD. (104 pages, 16 chapters.)
Here is the link: https://www.datasciencecentral.com/profiles/blogs/fee-book-applied-stochastic-processes One has to register an account on the site in order to download it.
Hopes this help, Vincent