About sales and local tax

But we are buying the goods against cst

My 2nd question is if we buy goods from gujrat to mahatashtra and want to sell in gujrat what type of billing shoulb be thete.and the party from maharashtra will give c form

Even though you are purchasing the goods against you need to charge VAT from your customers in maharastra & you are not eligible for CST which you have paid in gujarat as input credit so you can project them as expenses in your profit & loss account.

I don't understand your second so please make it clear.

Shafic, 

When You purchase goods from other State CST will be applicable and when you purchase goods from Same State VAT will be applicable. In the case you mentioned When you purchased goods from Gujarat, You purchased it from different state whereas when you are selling it, you are selling it in the same state. Hence CST will be applicable in first case and VAT will be applicable in the second. 

Note : It Doesn't Matters from Where the Goods Originates. You have to look at The purchase or sale transaction for the current buyer or current Seller.

Hope it clears your Doubt!!

In this casewhat should i have to do for exemption of vat

Is there any rule that only cst will be charges

As per My knowledge, You don't have any option for getting any input credit whether it be CST or VAT. 

Wait for others reply if they have better Idea!
 

What would if purchase from other state and sell in my state

Shafic,

As I said earlier, It doesn't matters from where you purchase. Look at the current transaction for evaluating Whether it is CST or VAT.

As per my opinion,  you are required to charge VAT on sales whether you buy it from other states or from the local market. 

And there is no any option of aviling any credit of CST paid on inter-state purchases.

And at last same as harshad, wait for others reply if they have any better idea.