First of all we create matrix(5x5) where each of the 25 alphabets must be unique and one letter of the alphabet (usually J) is omitted from the table (as the table can hold only 25 alphabets). If the plaintext contains J, then it is replaced by I.

The initial alphabets in the key square are the unique alphabets of the key in the order in which they appear followed by the remaining letters of the alphabet in order.

After so , The plaintext is split into pairs of two letters (digraphs). Since Playfair cipher encrypts the message digraph by digraph. Therefore, the Playfair cipher is an example of a digraph substitution cipher.

You can also checkout caesar cipher encryption technique
caesar cipher encoder / decoder.

1. It is significantly harder to break since the frequency analysis technique used to break simple substitution ciphers is difficult but still can be used on (25*25) = 625 digraphs rather than 25 monographs which is difficult.

2. Brute force attack does not affect it.

3. Easy to perform the substitution.