When purchasing a resale property the purchase agreement will contain the details of the vendor and purchaser, the purchase price and details of the payment method.
It will also confirm that the title deeds (Escritura de Compraventa) are in the name of the vendor and this will be transferred to the purchaser upon completion of the sale.
Information of who is responsible for the taxes and costs involved in the transfer will also be detailed.
There will also be details of any penalties for non-compliance with the agreement for both the buyer and seller.
In the event that the property is still under construction or you are purchasing 'off plan' the purchase contract will contain similar details including further information regarding ownership of communal land, building permissions, projected completion dates, stage payments, etc.
Your Estate Agent should go through the purchase agreement with you and explain in the clearest terms any details you are not sure of. If you are not sure of any clauses in the agreement, then do not sign it. A good reputable estate agent will refer you to an independent solicitor for further advice.
You can still 'reserve' the property with a holding deposit until your solicitor has had the opportunity of checking the agreement prior to you signing. No reasonable developer or agent will refuse to refund a holding deposit in the event your solicitor discovers a legal reason why you should not proceed.