This is the 1702nd most frequent Russian word.
большого
The Russian word "большого" means "of big" or "of large" (genitive or accusative singular form of "большой").
Here, "большую" is the feminine form in the accusative case, modifying the feminine noun "книгу".
Я купил большую книгу для своего проекта.
I bought a large book for my project.
"Большими" is the instrumental plural form, referring to the plural noun "экспонатами".
Мы посетили музей с большими экспонатами.
We visited a museum with large exhibits.
"Большого" is in the genitive singular masculine form, modifying the neuter noun "внимания".