• Traditionally websites built with HTML, CSS, Javascript 
• And android apps with Java or Kotlin and ios apps with swift
• But in current times the speed to ship a product is what makes a company successful indeed it makes you more efficient 
• Hence there are many frameworks that have taken over which use to leverage your time 
• Frameworks to build web apps are React, Angular and Vue and frameworks to build mobile apps are Flutter, React Native and ionic
• We personally use flutter not because it's the best but we have our hands already dirty on it

Let's hop back to the restaurant analogy

•  it's the kitchen where the food is being cooked and all the materials are stored
• Similarly, all the data that you throw at the app {Like the number of likes on your profile photo} is very meaningfully stored in the database

• Databases are broad of two types SQL and no SQL you can search easily for their difference
• You should have a knowledge of how both of these databases work and at least be comfortable in any one of them
• The large company uses multiple databases according to their need so having broad knowledge on both the kind really helps
• You don't have to be a master in databases you just need to know the basic queries and the initiation process and schemas to make your own database and start the magic

• Have you entered a restaurant kitchen and started eating no right! 
• The job to serve the right food to the right person is of the waiter 
• Similarly, in a software product, the data stored has to be shown on the app to you like this amazing stash is being shown to you know
• This is the job of the API which shows up the information stored in the database in a very meaningful way to you
• it's responsible for showing the right message to the right people, Data encryption, process payments 
• And all the magical things that happen while using a piece of software 

There are a whole lot of frameworks out there to build API's 

Some of the popular ones are

1. Express-js {a framework on node-js}, 
2. Django {a framework based on python}, 
3. Rails {a framework based on Ruby}

You absolutely don't need to learn all the frameworks you just have to learn one and make a whole lot of projects in order to get the right practice 

We personally use express you can use any one of the many options available