How to call rest api webservices

Step 1 : Initially create connected app in salesforce.

here:
callback URL: https://login.salesforce.com/services/oauth2/callback
selected OAuthScope:Full access (full)

Now you can use consumer key, consumer secret for rest api.

Step 2: How to get access token:

Method	:	POST
URL	:	https://login.salesforce.com/services/oauth2/token
client_id	:	consumer Key from salesforce connected app
client_secret	:	Consumer secret from salesforce connected app
grant_type	:	password
username	:	restAPi@soliant.com (user id)
password	:	password + security token

Output

{

    "id": "https://login.salesforce.com/id/.....",

    "issued_at": "1435335550081",

    "token_type": "Bearer",

    "instance_url": "https://ap2.salesforce.com",

    "signature": "-----xyz-----",

    "access_token": -------xyz------"

}

Step 3 : How to call Rest API from Postman or other rest client

Insert / update

Method	:	POST
URL	:	https://ap2.salesforce.com/services/apexrest/webservices  (<instance_url>/services/apexrest/< urlMapping of class>)
Header1	:	Authorization
Value1	:	Bearer <space> <access_token>
Header2	:	Content-Type
Value2	:	application/json

Now select raw and write json in it like:

For insert contact

{

    "JSONString": {

        "attributes": {

            "type": "Contact"

        },

        "FirstName": "John",

        "LastName": "test",

        "Email": " testing @gmail.com",

        "Phone": "12121212"

    }

}

For update contact:

{

    "JSONString": {

        "attributes": {

            "type": "Contact"

        },

        "id":"00328000003KfhB"

        "FirstName": "John",

        "LastName": "testing",

        "Email": "testing@gmail.com",

        "Phone": "12121212"

    }

}