Included with the link provided had you read it.
With LTE on iPhone 5, you can browse the web, stream content, or download amovie at blazing-fast speeds. To see if iPhone 5 works with LTE networks in your country, refer to the chart below.1 For more details, contact your carrier.
GSM model: UMTS/HSPA+/DC-HSDPA (850, 900, 1700/2100, 1900, 2100 MHz); GSM/EDGE (850, 900, 1800, 1900 MHz)
Spain is not listed with the link provided, so more than likely LTE access won't work there but 3G and EDGE access should.
LTE is 4G the next faster generation of cellular speed (after 3G ,the current )
The iPhone 5 purchasedi n Singapore will NOT have warranty in Spain ,the warranty is not international and available only in Country of purchase .
In the event of any issues you would have to return the iPhone to Singapore for any service ,warranty or post warranty .