Create ur own salesforce Developer org and then start beginner trialheads related to Apex and visualforce Page. Link : https://trailhead.salesforce.com/en/trails/force_com_dev_beginner
Along with this,you can also go through various blogs related to Salesforce so that u will get more idea. For example: http://salesforceglobe4u.blogspot.in/
Create ur own salesforce Developer org and then start beginner trialheads related to Apex and visualforce Page.
Link : https://trailhead.salesforce.com/en/trails/force_com_dev_beginner
Along with this,you can also go through various blogs related to Salesforce so that u will get more idea.
For example: http://salesforceglobe4u.blogspot.in/
Look for https://angelsoftech.com/learning/sfdc/basic/salesforce-architecture