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Ankit SatnalikaAnkit Satnalika 

Lead Conversion in Salesforce.

How Lead conversion takes place in Salesforce ?
Robert KnippRobert Knipp
You convert a lead by opening the lead record, then click the "convert" button. That works in Classic and Lightning. The Lead is converted into a account and a contact and an opportunity - with the option to skip all creation steps and adding the information to existing records. The lead status can also be selected. It needs to be "closed" status, by default it is "Closed - Converted".
For more info:
Trailhead: https://trailhead.salesforce.com/content/learn/modules/admin_intro_opptys_leads 
Field Mapping: https://help.salesforce.com/articleView?id=lead_conversion_mapping.htm&type=5 
Deepali KulshresthaDeepali Kulshrestha
Hi Ankit,

When you convert leads, Salesforce creates accounts, contacts, and, opportunities using information from the leads you’re converting. Salesforce moves any campaign members to the new contacts, and the leads become read-only records. If existing accounts and contacts share the names specified on the leads, you can choose to update the existing accounts and contacts. Salesforce adds information from the lead into empty fields; Salesforce does not overwrite existing account and contact data.

For more information refer to these links:
https://help.salesforce.com/articleView?id=faq_leads_what_happens_when.htm&type=5
https://salesforce.stackexchange.com/questions/42212/what-happens-when-a-lead-is-converted
https://success.salesforce.com/answers?id=90630000000gyYHAAY
https://trailhead.salesforce.com/en/content/learn/modules/admin_intro_opptys_leads/admin_intro_opptys_leads_leads

I hope you find the above solution helpful. If it does, please mark as Best Answer to help others too.

Thanks and Regards,
Deepali Kulshrestha
Gary RalstonGary Ralston
Hey Ankit,

The lead conversion process can be initiated by accessing the lead record and selecting the 'Convert' button on its highlight panel. Upon conversion, Salesforce create an account, contact, and optionally an opportunity using information from the lead. If the lead was a part of a campaign, the campaign member record will be linked to the new contact. During this process, you can choose to create new or use existing account, contact, and opportunity. Once the lead has been converted, the lead record will become read-only.

Check out the article at https://arrify.com/convert-lead-in-salesforce/ to understand the process of converting a lead. This guide illustrates how to convert a lead into Accounts, Contacts, and Opportunities.