Salesforce will keeps track of which objects you use and how often you use them, and arranges the search results accordingly. Objects you use most frequent will appear at the top of the list. If you do not see the object, click Search All at bottom.
After you search something in Salesforce, you will see Options in search result page. From here, you can restrict search result only to records you owned.
Salesforce search is case-insensitive for the whole data.
Wildcards and Operators
You can use the * (asterisk) and ? (question mark) wildcards to refine results. Use * to match one or more characters, or ? to match a single character. For example, searching for bob jo* finds items with Bob Jones and Bob Johnson, and searching for jo?n finds items with john and joan. You can also use the AND, OR, AND NOT, ( ) (parentheses), and " " (quotation marks) operators to refine results.
Sample: johan AND (singapore OR Indonesia); please note: operator support is case-insensitive.
See salesforce documentation on Operators for more information.
But, my search result still do not shown records from a custom object. Why? This is usually happened because administrator do not create tab for that object. That is why Salesforce search function will not search custom objects if the objects don't have tab. For more info related to this, read this blog Global Search Result on Custom Object.
If your company have Chatter enabled, Global search also returns Chatter feed result. From above screenshot, click "Search Feeds" link. This results include all relevant public posts, including posts from people you are not following and from public groups you are not a member of. In other words, Global search return more feed information than when you search and individual feed (Chatter home feed, record feed, group feed).
To search only from a particular feed, use the "Search in Feed" magnifying glass, if you type more than 1 word, it will search words appear together, as well as they appear separately.
Chatter Feed in Home tab
Feed in Chatter tab
Another way to search in Chatter using Topic, it will show all post or comment tagged with a topic, even from people you are not following, or group you are not a member of. You also can follow the topic, so when someone use that topic, it will appear in your feed.
Bookmark is another way to follow a post, so you can easily looks for that post interested you from Chatter Bookmarked link.
Reference: Global Search Result on Custom Object
Last update: 8 May 2016