What is the difference between God and Devi-Devta or are they same?
Yes, there is a difference between Gods and Devtas.
In Hinduism, the Trimurti is the God. Bhagvatam further clears that Krishna is the supreme God (verse here).
Devtas are God's helpers. All the Devtas are given some jobs. They are thus classified into each of their own department.
Like Indra Dev looks into weather. Surya Dev is responsible for giving energy and light to plants, animals etc. Vayu Dev takes care of the flow of wind etc.
Devas also take in return materialistic things. Like in Yagnas etc, we offer Aahuti to devas. The people of Mathura gave fruits and other stuff to Indra Dev, so that he can protect them from rain and thunder. This practice, though, was condemned by Krishna himself because taking something forcefully for not harming them is bad. Things given by will can be accepted. Anyways, offering anything materialistic to Devas should be avoided.
You can further imagine it this way:
The entire universe is the office. Trimurti is the founder of the office. Devas are the workers/managers of specific departments.
I would also like to clear a common misconception that there are 33 crore devis/devtas. There is nothing like that. Crore means categories. People started thinking of crore as a number, and so did the confusion arise. There are devtas of 33 categories - 33 departments. They are NOT 330 million in number.
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