Below are the basic topics and tips for Regex with examples
(1)^The- Its matches and string that starts with the
Example:- The crackyourinterview sites has regex values

(2)End$- Its matches a string that ends with world End
Example:- this is now end

(3)^The End$-Its matches a string that start with "The" and end with "End"
Example:- The data in crackyourinterview has End

(4)data- Its matches the world given
Example:- Crackyourinterview have data in it

Quantifiers? ?* + ? and {}

(5)abc*- Its matches string that has ab followed by zero or more c
Example:- ab,abc,abcc,abccc

(6)abc+- Its matches string that has ab followed by 1 or more c
Example:- abc,abcc,abcc

(7)abc?- Its matches string that has ab followed by zero or one c
Example:- ab,abc

(8)abc{2}- Its matches string that has ab followed by two c
Example:-abcc

(9)abc{2,}- Its matches string that has ab followed by two or more c
Example:-abcc,abccc

(10)abc{2,5}- Its matches string that has ab followed by two upto 5 c
Example:-abcc,abccc,abccccc

(11)a(bc)*- Its matches string that has followed by zero or more COPIES of sequence bc
Example:-abcbc,abcbcbc

(12)a(bc){2,5}- Its matches string that has followed by zero or more copies of sequence bc from 2 to 5 times
Example:-abcbc,abcbcbc,abcbcbcbc

OR operator? ?| or []

(13)a(b|c)- Its matches string that has followed by b or c
Example:- ab,ac

(14)a[bc]- Its matches string that has followed by b or c
Example:- ab,ac

Character CLASSES? ? d w s and .

(15) d- Its matches a single character that is a digit
Example:- one1data,keepit1data,key2234

(16) w- Its matches alphanumeric character plus underscore
Example:-crack_yourinterview

(17) s- Its matches whitespace character(includes tabs and line breaks)
Example:- , ,

(18). - Its matches any character
Example:- a,cd,csd,fdf

d, w and s also present their negations with D, W and S respectively