The verb पाना can have many meanings, such as “to get, to obtain, to win, to earn”, etc.
However, it is very commonly used as a verbal auxiliary with the sense “to manage to do”.
When used as a verbal auxiliary, the verb has the following form:
[verb stem of main verb] [inflected form of पाना]
पाना inflects according to person, number, gender, tense, mood, etc. All of the inflection is in पाना; the main verb always appears as bare stem.
मैं पूरा खाना नहीं खा पाया – “I couldn’t eat the entire meal”
हिंदी बोल पाना बहुत मुश्किल नहीं है – “It’s not hard to manage to speak Hindi”
मैं दौड़ को ख़त्म नहीं कर पाऊंगा – “I won’t be able to finish the race”
It is similar to the verb सकना (“to be able”) since both verbs can express ability. However, पाना often has the sense of conveying success, versus ability.
मैं पुरे खाने को नहीं खा पाऊंगा – “I won’t be able to eat the entire meal”
The former sentence doesn’t convey an absolute inability, but a failure in one instance.