A custom app in salesforce is a collection of tabs, objects, etc. that function together to solve a particular problem.
Console apps in Salesforce are a tab-based workspace suitable for fast-paced work environments. These help to manage multiple records on a single screen, to reduce time spent clicking and scrolling to find, update, and create records quickly.
If you are interested to learn Salesforce from experienced instructors, I recommend this Salesforce Certification Course by Intellipaat that provides Instructor-led training, hands-on projects, and certification.
Also, check out this video on Salesforce:
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