Free API with Client id and Secret for testing purpose

 

Client -id 3MVG9JJwBBbcN47KTf38mTZCYZ1YdXGThRuFITMDG8JaLF03QQtS7v6L1vr4U7qwjWL62.8IL5lZI1br3DPjn

Client Secret-

C9BBBB41A2F737F46FAE51CE4D25F1E0EEBE14DA505F60D3EB12F0541CFD5A47

Token url- https://orgfarm-33b4115c6b-dev-ed.develop.my.salesforce.com/services/oauth2/token

Callback url- https://sfdcquestion.blogspot.com/

you can configure these these details in your code or any api tool

With the help of these above credentials you will get access token 

Option -2 you can also test in via post method and get accesss token:

like in this below image:

We can also get the record by using the get method . use the Instance url , and append some details in the url and add the bearer token value which got when i used previously .

Get URL- 

https://orgfarm-33b4115c6b-dev-ed.develop.my.salesforce.com/services/data/v64.0/query?q=select name from account order BY name limit 4

then click on send button then you will get the response with 4 account record.