how do you check for vaccum leaks at Intake manifold?

To find a vacuum leak I use a piece of white sewing thread or string, a heavier gauge depending on where you will be using it, and drag it around areas where I think the leak might be. Once it gets near the are where the leak is, it generally gets sucked in and you can then identify the extent to which the leak exists.

can you send me a picture showing how to use the string to check for vaccum leak.

I don't have a picture to show you. Just get a string, sewing string of a nylon or higher strength is good, and use white so you can see it.
Drag it around areas where intake pieces meet and are gasketed together such as the intake manifold and where it meets the throttle body or intake ports. Try around vacuum lines. When you drag it by a leak it will go towards it kinda like they way they used to put streamers on fans in stores to show how much aior they blow...but the opposite. It will move in towards the vacuum leak and you can use it to find exactly where the leak is by how hard it is tugging on the string. Sorry I don't have a picture.