Dear Mordadi

it is very simple, just write the symbol ">", then, write the sequence of your interest. for example

>DRHTFKHJDHSA..........etc

the, preferably store your data as txt format file.

best regards

Thanks dear mohammed

After store txt format how convert it to fasta?

txt format is considered as a readable file in many bioinformatics tools. Nevertheless, you can convert the txt format extension into fasta format extension using any freely downloadable extension changer software

best regards

I want that bioinformatic tools dear Mohammed. 

Thanks Kunal

MEGA work with data bases?

My peptide is not in databases.

My means about any possible fasta format is amino acids have different codon so a peptide can have different nucleotide sequences,

My dear friend Mr Jodati wrote a very simple software for me to doing this.

I described it in my project toxin-antitoxin.

I hope it be useful for other researcher.

With best wishes. 

Many thanks