Q:

How to get data from Google Analytics using google apis?

I am getting the data in Google Api Explorer now How can I get the data outside the api explorer. E.g. Postman
I am using Services > Google Analytics API v3 > analytics.data.ga.get
Do I need access token to get the data if yes then how ?

A:

I've not used Postman but it all depends on your use case for the data and the base code you are coding in. We can't tell you "how" to code it exactly as it is up to you depending on your needs.
For the V3 API, you can use their Hello Analytics library to access the information. It shows some examples for:

Python
Javascript
PHP
Java

Google recommends moving to their v4 version of the API as it has more features and will be the API which has new features implemented. Both have documentation to get you started.

Do I need access token to get the data if yes then how?

Yes, you will and the quickstart guides explain how you set these up.
Have a read through the docs, get started with the example script in the language you are most comfortable using. If you get stuck then come back an open a new question (if it is not answered already) with what you want to achieve, your code which currently is not working and what it should be doing.
Good luck!

