What is the best way to start an informal and a formal letter please tell experts

Dear Student,

The starting of a formal letter depends on the topic of the letter. However, in an informal letter you can start in a friendly manner.
Given below are some examples.

• FORMAL LETTERS
• I am writing this letter to express our gratitude to you for... (formal letter of thanks)
• I am writing this letter to seek your immediate help. (formal letter regarding misplacement of a belonging)
• I am writing this letter to bring to your attention the state of the local park in our area.(formal letter about a public place in the city or your locality)
• I am writing this letter to draw your attention to the deteriorating law and order in our locality. (formal letter to the police)
• INFORMAL LETTER
• Time does fly and I can't imagine it is already three months since I last wrote to you.
• It is indeed a joy to be writing this letter to you.
• I am excited to share with you all the new things happening in my life.
• Surprise! Surprise! I am here to converse with you.

The format and examples of both formal and informal letter are provided on the website. Refer to the website for the same.

Regards.