you can use sales force help https://developer.salesforce.com/page/Integration and use http://www.webservicex.net/new/Home/Index for soap open source files are availble
take rest integration for any open source http api gateways for traill .
Hi THUNDER CLOUD, You will first start with Linkedin integration, i am done lots of integration salesforce to 3rd party but Linkedin is best for Starting . follow these link https://developer.linkedin.com/docs/signin-with-linkedin
Day by day i am become a fan of TraillHead. Now learning in salesforce to much easy as compare to our time. The Salesforce Trailhead now offers a fun way to learn everything related to Salesforce Integration
you can use sales force help https://developer.salesforce.com/page/Integration
and use http://www.webservicex.net/new/Home/Index for soap open source files are availble
take rest integration for any open source http api gateways for traill .
Regards
Harish.R
You will first start with Linkedin integration, i am done lots of integration salesforce to 3rd party but Linkedin is best for Starting .
follow these link https://developer.linkedin.com/docs/signin-with-linkedin
Thanks & Regards
Jasveer Singh
Apex Integration Services
1) https://trailhead.salesforce.com//module/apex_integration_services?utm_campaign=trailhead&utm_source=sfdc&utm_medium=chatter-success
Apex Integration Overview
https://trailhead.salesforce.com//apex_integration_services/apex_integration_callouts
This module will Describe the differences between web service and HTTP callouts and Authorize an external site with remote site settings
Apex REST Callouts
https://trailhead.salesforce.com//apex_integration_services/apex_integration_rest_callouts
This module will describe about Perform a callout to receive data from an external service and Test callouts by using mock callouts
Apex SOAP Callouts
https://trailhead.salesforce.com//apex_integration_services/apex_integration_soap_callouts
This module will describe you about Generate Apex classes using WSDL2Apex and Perform a callout to send data to an external service using SOAP with Test callouts by using mock callouts
Apex Web Services
https://trailhead.salesforce.com//apex_integration_services/apex_integration_webservices
This module will Describe the two types of Apex web services and provide a high-level overview of these services. Create an Apex REST class that contains methods for each HTTP method and Invoke a custom Apex REST method with an endpoint
You can also check below post I hope that will help you
1) http://amitsalesforce.blogspot.com/search/label/Rest%20API
2) http://amitsalesforce.blogspot.com/2016/04/rest-api-in-salesforce-execute-rest-api.html
Let us know if this will help you