What is difference between screen flow and auto launched flow?

Screen Flow-Requires user interaction, because it includes screens, local actions, steps, choices, or dynamic choices. Screen flows don’t support Pause elements.

Autolaunched Flow-Doesn’t require user interaction. This flow type doesn’t support screens, local actions, choices, or choice sets

What is invocablemethod?

@InvocableMethod annotation is required for calling any apex method from flow.

For Flow, care should be taken to retrieve records once and then loop through them rather than repeatedly retrieving records through multiple loops (this is equivalent to not performing SOQL within a loop).

Difference between flow and process builder?

Process Builder Salesforce Flow
Can’t be used to delete records. Can be used to delete records.
Not all objects are supported by Process Builder. Many objects are accessible using Salesforce Flow. For example – OpportunityContactRole, UserDevice, etc.
Can be triggered when a record is created or edited. Can be triggered when a record is created, edited, or even deleted.
Can’t be triggered after a successful login. Can be triggered when a user successfully logs into Salesforce.
Not possible to save the newly created record ID (If it is created using the Record Create element). Possible to store the newly created record ID in a variable; so that, you can reference it in a flow later.
Good for the intermediate use case. Much more power to implement complex logic.
Can’t be used to capture user input(s). Can be used to capture the user input(s) and later process it based on your business use case.
Can be Schedule to run daily, weekly or once.

Can we change the data type of variable once we have created in lightning flow designer?

No we cannot change the data type once created

What are the ways in which flows can be launched?

A Screen Flow can be launched using one of the following
  1. Using Flow Component in Lightning Record Page
  2. Using Flow Component in Lightning App Page
  3. Using Flow Component in Lightning Home Page
  4. Using Flow Component in Lightning for Outlook
  5. Using a Custom Button
  6. Using a Custom Link
  7. Embed a Flow in Visualforce Page
  8. Using Login Flow
  9. Using Inline Visualforce Page
  10. 10.Using Quick Action

Can we query process Builder / Flow

No we cannot query but we can see details through workbench ->Info–> MetaDataTypes & Components>Flow>Components.