
According to https://www.oxfordlearnersdictionaries.com one meaning for the adjective free is – costing nothing
Sentences with free can look like this:
Something is free…
My coffee was free.
Or we can do something for free…
I can watch for free online.
Maybe you can guess the grammar already.
A noun is free
These baseball tickets were free!
We verb for free
We can watch the game for free.
*If we get something (a noun) we can say for free because get is a verb.
I got these shoes for free!
Alex works at the theater so he gets tickets for free.

*NOTE*
I received a comment from Warsaw Will that pointed out that…
…after a verb, the adverb “free” is just fine without “for.”
You can eat free in my restaurant whenever you like.
This is a natural example of a verb (eat) followed by the adverb free without the preposition for.
I wanted to make a simple example that ESL students could understand but I shouldn’t have said that…
…we need to say for free because get is a verb.
This is not true. For me personally using FOR FREE with a verb is natural, but we don’t have to. The example below is also perfectly acceptable.
I got these shoes free!
Thanks again to Warsaw Will for the constructive feedback on my post. You can see his English blog @ http://random-idea-english.blogspot.com/
Free @ oxfordlearnersdictionaries.com
https://www.oxfordlearnersdictionaries.com/definition/english/free_1?q=free
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