A girl is sold across the narrow sea
Viserys Targaryen trades his sister Daenerys to Khal Drogo for an army. What he buys instead ÔÇö over a year of grass, cruelty, and unexpected love ÔÇö is her: a frightened thirteen-year-old who discovers she is not frightened of fire, and who will outlive him by rather a lot.
The fuller tale
Viserys Targaryen had been selling the family's future for a decade ÔÇö begging in the Free Cities, calling himself a king in rooms where people laughed at him ÔÇö and in Pentos he found a buyer. Illyrio Mopatis arranged a marriage between his thirteen-year-old sister and Khal Drogo, and the price was an army.
Daenerys Targaryen was handed over at a wedding where twelve men died and nobody remarked on it, to a man she could not speak to, in a culture that had no place for what she had been. What happened over the following year is the part the histories are bad at, because it is not an event: she stopped being afraid, in stages, and each stage cost her something.
Her brother could not adapt at all. He kept threatening a khal in a khalasar, kept demanding his crown, and eventually got one ÔÇö molten gold poured over his head in front of his sister, who watched and did not look away and said afterwards that he was no dragon, because fire cannot kill a dragon.
What she was buying
The bargain that was supposed to make Viserys a king made Daenerys something the world had no ready category for: a Targaryen who had been sold, had survived it, and had watched the last man with a claim ahead of hers die badly and felt nothing.
Everything she does afterward is coloured by having been property. It is why she frees slaves and why she cannot stop, and it is also why she has so little patience for anyone who tells her that a thing cannot be done.
Elsewhere in the wiki
 See the world as it stood in 298 AC What became of it  if an ending is written, it is here. Spoilers.
The chronicle records no ending here ÔÇö or none the maesters have set down.