Best Methods and Sites to Compare Integrated Circuits (ICs) and Datasheet Parameters

Is there a site or any technique to compare Integrated circuits?
Or which values on datasheets we need to compare to check if they may be used instead of each other?

Thanks.

Some items on a data sheet are considered critical, some aren't. Unfortunately on on devices that are nominally identical, the manufacturers may not agree on on which of those items to specify. The conditions of test can be different to your application, so comparison can be difficult. I know of no site that allows you direct comparisons.

There is a series of excellent articles on reading datasheets on this web site by Elizabeth Simon. I would start out here:
https://www.eeweb.com/author/elizabeth-simon/

The very first one is on page 4.

There are thousands, millions of ICs on the market.
One solution is to Google the example string:

"CD40106 equivalent".

A good site is this:

https://www.digchip.com/

or this

http://www.dcdcselector.com/en/replacement

Greetings
Giovanni