Does your everyday life include a bunch of people pestering you over the phone, especially if you aren't paid or in any way required to deal with them? Do you want to avoid having to answer or even decline calls from salesmen, scammers, or the crazy ex that's been bugging you since that one drunk summer night in 2011? Naturally, Brits can sign up for something called the Telephone Preference Service which does a solid job preventing reception of unwanted calls, but it's neither perfect nor are identical services available globally. So, what can Android users worldwide do about the nuisance of the modern era that are annoying abusers of telecommunications services? Why of course - they can learn how to block a number and stop all of those unwanted calls.
The very process of blocking a number on an Android phone depends on the brand, i.e. manufacturer of the said device, but usually, venturing into the settings app and navigating to the Device > Call > Call Rejection menu does the trick on a number of phones. Here you can not only create a so-called rejection list of numbers that you don't want to see lighting up your phone screen anytime soon, but also optionally create a rejection message to automatically send to your undesirable callers if you'd like them to know they're on your rejection list or just constantly keep telling them you're "in a meeting" until they get the hint. The same can be done from the contacts list by opening a pesky contact, tapping the menu button, and selecting "Add to Auto reject list", which is a Samsung-specific feature, but works in a similar manner on many other phones. E.g. owners of LG devices can accomplish this by tapping the three dots in the top right corner of their main phone screen, then navigating to Call Settings >Call Reject > Reject calls from. Similar to Samsung, blocking a number on an HTC phone can be done by long-pressing a contact from your call history or contacts list and selecting the "Block contact" option.
Naturally, if you can't find the option in one of your device's many menus or it simply isn't supported by your phone, there's a plethora of caller ID and blocking apps that can do the work for you in a manner that's just as simple. Truecaller is one of them that has been rather popular in recent years, but if you're looking for an alternative, there's plenty of great blocking apps to choose from on Google Play Store. These days, even some anti-virus solutions like Avast offer the call-blocking function.