I have forgotten me Apple ID password now what I have to do for this purpose

Read this,

If you have forgotten your Apple ID password – Apple Support (UK)

And if you really meant - Computer Password

Reset Computer Password 

Intel Computer

1 - Restart computer and immediately hold Command + r keys

2 - Top Tool Bar >> Utilities >> Terminal

3 - Type resetpassword as one word and no spaces

4 - Press Return key

5 - Follow the prompts and remember the New Password