[Eric]

It depends on a few factors:
If it's a master detail relationship and you want to roll up a number type field (number, currency, percent), you can create a roll up summary field on te parent.
Otherwise, create a field on the parent as needed and use this free package:
https://github.com/afawcett/declarative-lookup-rollup-summaries

[Eric]

Hi Ayush,

This article should help you:
https://help.salesforce.com/articleView?id=workflow_time_action_considerations.htm&type=5

[Eric]

Hi,

There are a couple of ways:
1-In Salesforce, go to set up> Object Manager> Find the object and click on Fields & Relationships. You'll see the API names as well as whether the field is custom or standard
2-Go to https://developer.salesforce.com/docs/atlas.en-us.sfFieldRef.meta/sfFieldRef/salesforce_field_reference.htm and search for an object (ie Account). You'll have a list of all the standard fields and their API names
3-Use the API to extract objects and their fields. You can use the data laoder for this, or workbench, dataloader.io, there are plenty