Seems like the questioner was asking for a bit more than just an idea of conversion rates, so here is some background on how the pre-decimal currency worked.
4 farthings = one penny
2 halfpennies = one penny
tuppence = colloquial two pence
thruppence = colloquial three pence
240 pence = one pound
6 pence = sixpence (aka a tanner), or half a shilling.
12 pence = one shilling
two shillings = one florin
5 shillings = one crown
two shillings and sixpence = one half-crown
One guinea was latterly (and still is in horse racing) one pound and one shilling, although earlier in its history its value varied according to the value of gold. For about the last 200 years it has only been a unit of account rather than an actual coin.
Likewise the Sovereign was a gold coin nominally valued at a pound, but its true value was whatever the value of the gold in the coin was worth that day. Bullion coins such as the Sovereigns were an investment to be stored for their own inherent value, rather than as a coin to be used when going out to buy goods.
Other common units of currency were:
The mark (merk in Scotland) — a very common unit of account, and not actually ever a coin (in England). A mark was 13 shillings and 4 pence.
The way to write prices in pre-decimal currency was generally as follows:
£10 5/- Ten pounds five shillings
£10 5/6 - Ten pounds five shillings and sixpence
£10 5s 6d was equally valid.