Hey,
First of all you need to mention the college or university you are looking for because each and every college follows a different set of procedure. For slot booking.
Thank you.

Slot booking is different for different colleges. Please let us know which college you are upto.

Hello
For Slot booking for NIT & IIT admission.you get a website where you fill the College you want & you have to fill it in sequence.

Which exam is this for? JEE Mains I hope not as there is no slot booking open for it. The slot booking for JEE Main was to be done after filling the application form. As for VIT and BITSAT, the slot booking procedures are 

Click here to know about BITSAT slot booking

Click here to know about VITEE Slot Booking

Hey Fathima,

Students can book a slot while filling an application form. Students must follow the given steps to book their slots:

• Visit the official website. ( JEE Main 2018 )
• Then, click on “Click here” link to apply.
• Fill the application form carefully.
• After completion of fee payment, click on “Click here to Go Home” link.
• Then, click on “Select Date for Computer Based Examination for Paper 1” link.
• Select your exam date as per your preferences.
• After booking a slot, click on the “submit” button.
• Take a print copy of filled application form further details.

Well you just need to open the website of your exam conducting body .There you will find notifications regarding it and what steps you would be needing to follow for booking slot.

Don't worry it is very  easy step . So relax and do keep checking the for the notifications.

Hope you're asking about JEE mains
Students can book a slot while filling an application form. Students must follow the given steps to book their slots:

Visit the official website. (JEE Main 2018)Then, click on link to apply.Fill the application form carefully.After completion of fee payment, click on Click here to Go Home link.Then, click on Select Date for Computer Based Examination for Paper 1 link.Select your exam dateas per your preferences.After booking a slot, click on the submit button.Take a print copy of filled application form further details.
Thanks:)

Hi!

You simply login to the website of your exam conducting body and keep following the steps and they'll automatically show you where you want to book a slot and where. 

Once you have filled your form, the exam conducting body will contact you via email or sms or anything of the same sort and let you know all the steps to be taken.

So rest assured! and keep preparing.

All the Best!