how to check a string contain a specific character as begining SQL code example

Example 1: check if string contains substring sql

Declare @mainString nvarchar(100)='Amit Kumar Yadav'  
---Check here @mainString contains Amit or not, if it contains then retrun greater than 0 then print Find otherwise Not Find  
if CHARINDEX('Amit',@mainString) > 0   
begin  
   select 'Find' As Result  
end  
else  
    select 'Not Find' As Result

Example 2: sql where contains part of string

-- To find an exact string
SELECT * FROM [table] WHERE [field] LIKE '%stringtosearchfor%'.