The main Anglo-Saxon settlements in Britain date back to around 449 A.D.. The Angles, the Jutes and the Saxons were northern tribes, which, between the middle of the 5th century and the biginning of the 6th penetrated various parts of the country rather as bands of unco-ordinated adventurers than as an organized army. After a long struggle against the Romans and the Celts they were able to dominate England (late 6th century) and their line of kings lasted until 1066, when William of Orange came from Normandy and, in the battle of Hastings, won himself the throne. This date also marks the beginning of a profound transformation of Old English, Middle English was going to arise: many French words entered the language and important modifications were made; Modern English is in fact very different from its ancestor, OE being not intelligible to a Modern speaker.
Old English was an iflectional language, so word order was not so important as it is in Modern English. In Middle English, the three inflectional vowels of Old English became one, so most inflectional endings (such as case distinctions and verb conjugations) were lost.
Old English vocabulary is obviously Germanic, many Danish wrods were introduced during the reign of King Cnut, to, but the Norman invasion in 1066 brought an enourmuos quantity of French (romance) words into English, so that nowadays about 80% of the English vocabulary is romance, while its core (the most common, everyday word, including all the grammar words)words are of Germanic origin.

Before the invasion of these Northern warriors, Britain was inhabited by Celt peoples, such as the Scots and the Picts in the North and other peoples that were united by the Romans in the South. The Anglo-Saxon invasion meant the settlement of a whole people, whose language remained dominant in England, while the traces of the original Celtic language in English are very small.

Old English pronunciation [E1] [E2] [E3] [E4] is very different from Modern English. EVERY symbol must be pronounced.
There were seven vowel symbols and 16 consonant ones. The vowels could all be long or short; diphtongs were represented by diagraphs and double consonants were effectively pronounced as double.
Here is a table of Old English sounds and their spelling:

As to the consonants, they are pronounced as in Modern English with these differences:

for a table of phonetic sounds check this page [E1]

An example of Old English poetry

This is a very short passage from The Wanderer [E1] one of the finest elegies written in Old English [E1] [E2].

The Wanderer is preserved in the Exeter Book [E1][E3]. The author, speaks of an attack upon his people that happened in his youth, when his friends and kin were killed.
The structure of the poem is of four stress-lines of different lengths, divided by a caesura. Like most Old English Poetry, it is written in alliterative meter.