How to make Gmail in Android ask for user name and password as in laptop? In my Samsung Galaxy Grand whenever I select the Gmail icon, it automatically takes me into the inbox, it doesn't ask me to give credentials like we do in laptop/desktop.

So the problem is when somebody else wants to use my mobile, they are able to see my all inbox mails etc etc as soon as they choose the Gmail icon.

So I want it set so that when I access the Gmail icon in Android, it should ask me to give username and password everytime .
The solution to your problem is using an "App Locker", which lets you protect selected apps with a password (or pattern). Each time you want to open a protected app, you then have to first "unlock" it. There might also be solutions permitting you to keep the "unlock" cached, e.g. for a confugured time span or place (e.g. when home) -- but as I don't need any app-locker I never remember which app offered that.

Examples for such app-lockers are Smart App Protector(App Lock), supporting password, pattern, and even gesture unlock, and Smart AppLock (App Protector):

 
Smart App Protector and Smart AppLock (Source: Google Play; click images for larger variant)