Old Norse names are cited in their Old Norse forms. This requires two unfamiliar letters (still used in modern Icelandic and Faroese), called ‘eth’ (ð / Ð) and ‘thorn’ (þ / Þ). The first of these is pronounced as the ‘th’ sound in ‘the’, for example in the name of the king of the gods, Óðinn (Odin). The second is pronounced as the ‘th’ sound in ‘thorn’, as in the name of Þórr (Thor).
Scholars usually pronounce Old Norse words as if they were modern Icelandic. Stress falls on the first syllable. Most consonants are pronounced as in English (with ‘g’ always hard as in ‘gate’, but ‘j’ pronounced as ‘y’ as in ‘yes’). So: ‘Gerðr’ = ‘GAIR-ther’ (the capitals show the stress).
Vowels are also pronounced as in English when short, though short ‘a’ is like ‘a’ of ‘father’, not as in ‘cat’. ‘y’ is the same as ‘i’: ‘Gylfi’ = ‘GIL-vee’. ‘ll’ is pronounced like ‘tl’: Valhöll = VAL-hertl.
Long vowels (marked with an acute accent) are mostly just a longer version of the short ones, though ‘á’ is like ‘ow’ as in ‘how’. The goddesses are collectively called the Ásynjur = ‘OW-sin-yur’.
Diphthongs are somewhat different: ‘ei’ or ‘ey’ is ‘ay’, as in ‘hay’, so Freyr = ‘FRAY-er; ‘au’ is a little like ‘oh’, but longer than in English. ‘draumar’ (dreams) = DROH-mar.
‘æ’ is pronounced ‘eye’, so the ‘Æsir’ (the main group of gods) = ‘EYE-seer’.
‘ö’ and ‘ø’ are like German ‘ö’: something like ‘er’. Thus ‘Jötunheimar’ (the lands of the giants) = ‘YER-tun-HAY-mar’.