making passive voice

Kono hon wa ookuno hito ni yomareteimasu : This book is read by many people
kono : this
hon : book
ooi :(adjective) many, much,
ookuno: "ooku"is stem,"no" connects the adjective with noun
hito : person, people,human
ookuno hito : many people
ni : by
yomu : read
(yoma-nai,yomi-masu,yomu,yomu-toki,yome-ba,yome,yomou,yonda)
reru/rareru : is attached form a of verb-conjugation and makes it passive voice
yoma+reru : is read

Kono hon wa ookuno hito ni yomareru : this, book, many people, by , is read.:This book is read by many people.

shiteiru : literaly means "is / are doing". Sometimes "shiteiru" describes not only the action but also situation
When "shiteiru" attached to verb, the verb should be form b (-masu form).
And sometimes verb should be with euphonic change.

yomu +shiteiru : yomi+ -teiru : yondeiru : is reading

yomu+rareru+shiteiru : yomareteiru : is been read, is read

and , lastly, "masu" is attached and the sentense becomes polite.

yomareteiru+masu : yomareteimasu. : is read

Kono hon wa ookuno hito ni yomareteimasu : This book is read by many people.

For example, let us try with "miru(see)".

miru: see, look,watch
(mi-nai, mi-masu, miru, miru-toki, mire-ba, miro, miyou,mita)

miru+rareru : mirareru
mirareru+shiteiru : mirareteiru
mirareteiru : mirareteimasu.

Anata wa dareka ni mirareteimasu : You are watched by someone

dareka : someone
ni : by