Does an internship really help? And if it does, how much internship experience would be sufficient to get a good job?

INTERSHIP IS THE BASIC KNOWLEDGE OF INDUSTRY TO MAKING PERFECT MEMBER OF INDUSTRY.

for a good job on the basis on Internship is subjected to the plateform at which internship conducted and education must be matched.

It does. Should the company you're spending your internship will be impressed of your work, they might actually hire you.  Other companies also consider internships as work experience. Afterall, all they want most is to know you already know how to do the job they're seeking. So, internship really is a good thing to consider.