The most awaited feature Global search is finally here. Although there are addons available in market for global search, check this post for details, but this feature was not available OOB. Actually this feature was already released in MS CRM 2013, CRM for tablet client, but MS CRM 2015 introduced this feature for web client as well. When you will login to CRM, you will see a search text box in top navigation bar, where you can enter your search string then CRM will list out all the configured entity records if found. Once you have result you can also filter it based on specific entity using Filter With dropdown next to search text box.
Global search can be configured by navigating Sittings-> Administration->System Settings->Set up Quick Find. We can include up to 10 entities for global search using select button (Although you can add more than 10 entities but it won’t allow you to save if you have more than 10 entities listed under Selected Entities.
You can change the order of entities in which order you want to see the result. Internally global search use quick find column to search data.