A couple of stupid questions about MSSQL indexes?

Question

SQL Server

Good day to all!
Faced with the problem of high-speed performance of the database. It was decided to create indexes, but questions arose about their expediency.
The first question: there is a table to which data is constantly written and from which data is constantly read. The ratio of operations is 2/3 - reading, 1/3 writing. But there are situations when the data has just been written to the database and in a second it is already being read from there (this is the architecture, I can’t influence it in any way). The percentage of such operations is about 20%. How justified is the use of indexes in such cases?
And the second question: how fast are the indexes updated and what will happen if the data has not yet got there? Those. I'm interested in a brief overview "on the fingers" of how SQL will search for data in the database and enter it there.

Answer 1

Indexes will be justified if there are more reads than writes. Indexes are updated immediately.
About the expediency of creating and which indexes - the DataBase Engine Tuning Advisor will help