Is there any level or tiers in conferences or all conferences are of same level? Is there any tiers or levels for conferences? and if yes on which basis people and authors can decide that a particular conference is of Tier 1 and another one is Tier 2 ?
The Australian Research Council (ARC) publishes a comprehensive ranking of journals which classified each as A*, A, B or C. This list can be found here.

The best way, however, is to talk to researchers or faculty members from the relevant field. I would be surprised if any researcher worth their salt didn't know what the main conferences are, each conference's preferences and biases, or what notional level of prestige is associated with each.