Prayer and Offerings ?

When making offerings and or prayers do you pray to certain gods for certain things such as; when blessing your food, or the day? What would a prayer sound like? Do you have to pray at your home alter every time you pray or can you pray when you're out and about?

You can pray whenever and wherever you want, and in your own words. Obviously you will address Agathe Tyche for prosperity, Asklepios for health, and so on. My daily prayers are specifically addressed to Hestia, Hekate, Asklepios, and Tyche, with words like "Come, blessed Asklepios. Accept this libation and my thanks for my continued health. May I remain under your protection."

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Plato ends the dialogue Phaedrus with Socrates, who has been walking in the country with Phaedrus, suggesting that they should offer a prayer to the local spirits before going home:
"Dear Pan and you other gods who inhabit here, grant that I may become inwardly beautiful, and that my external circumstances may further my health. May I consider the wise man to be rich, and grant me no more wealth than a moderate man can cope with."

In the 15th century, George Pletho wrote this prayer:
O blissful Gods, let me not cease to owe you gratitude for all the good things I receive. Let me not neglect to serve the common good, and consider that to be a benefit to myself. Let me not be the cause of anything evil, but rather of as much good as I am capable of, so that I may become blissful in your likeness."

Tyberious wrote:When making offerings and or prayers do you pray to certain gods for certain things such as; when blessing your food, or the day? What would a prayer sound like? Do you have to pray at your home alter every time you pray or can you pray when you're out and about?

DavidMcCann has answered well, and with good examples and resources – LABRYS is a very reputable organization – I've been in acquaintance with some of their leadership. 

As far as the 'sound' of a prayer – this is something that takes some study and practice. There is a kind of je ne sais quoi tone and phrasing used for classical Graeco-Roman prayers that will eventually come with exposure to them in reading. A good readthrough of the shorter/non-narrative Homeric Hymns will give you a good feeling for typical prayers. 

With time, it should come more naturally, and it will be possible to pray impromptu. 

Prayer outside of formal worship is not as typical in Olympian religion as it is in, say, Christianity, where personal prayer is very common. Nevertheless, it is certainly not unheard of.