• SOSL (Salesforce Object Search Language) is a search language in Salesforce, we can search in multiple objects at same time using SOSL. In SOQL, we can query only one object at a time but in SOSL, We can search for some specified string in multiple objects at the same time.
• SOSL query begins with the required FIND clause.
• The search string should be at least two characters long.
• SOSL is used if we don’t know in which object the data is present.
• We can mention in which fields of all the sObjects,we want to search for the string specified. Suppose you have to performed search on two objects Account & Contact. Then you can mention like, for list returned with Account results only (Name, Industry) fields should be returned, and for Contacts results (firstName, lastName) should be returned.
• We can retrieve multiple objects and field values efficiently when the objects may or may not be related to each other.
• We can query only on fields whose data type is text, phone and Email.
• The result of SOSL is a list of lists of sObjects.
  The returned result contains the list of sObjects in the same order as order mentioned in SOSL query.
• If a SOSL query does not return any records for a specified sObject type, then search results include an empty List for that sObject.
• We can use SOSL in classes but not in Triggers.
• We cannot perform DML operation on search result of SOSL.

Here in below example, there is a input text box and a command button which will search for the entered string in two Objects Accounts and Contacts and returned result will be shown in the page block tables.

Visualforce Page:

<apex:page controller="SampleController">
    <apex:form>
        <apex:inputText value="{!searchStr}"/>
        <apex:commandButton value="Get Records Using SOSL" action="{!Search}"/>
        <br/>
        <br/>
        <apex:pageBlock title="Accounts">
            <apex:pageblockTable value="{!accList }" var="acc">
                <apex:column value="{!acc.name}"/>
                <apex:column value="{!acc.Type}"/>
            </apex:pageblockTable>
        </apex:pageBlock>
        <apex:pageBlock title="Contacts">
            <apex:pageblockTable value="{!conList}" var="con">
                <apex:column value="{!con.name}"/>
                <apex:column value="{!con.email}"/>
            </apex:pageblockTable>
        </apex:pageBlock>
    </apex:form>
</apex:page>

Apex Controller:

public class SampleController {
    Public List<Contact> conList {get; set;}
    Public List<Account> accList {get; set;}
    Public String searchStr {get; set;}
    
    Public void Search(){
        conList = New List<contact>();
        accList = New List<account>();
        List<List <sObject>> searchList = [FIND :searchStr IN ALL FIELDS RETURNING  Account (Id,Name,Type), Contact(Name,Email)];
        accList = ((List<account>)searchList[0]);
        conList  = ((List<contact>)searchList[1]);
    }
}

Output: