How do you dial a land line number in the Republic of Ireland?

That depends on where you're calling from.

Within Dublin, just dial the subscriber number (usually 7 digits). Elsewhere in the Republic of Ireland, dial 01 followed by the subscriber number. Outside the Republic of Ireland, dial +353 1 followed by the subscriber number.

(The plus sign means "insert your international access prefix here." From a GSM mobile phone, you can enter the number in full international format, starting with the plus sign. The most common prefix is 00, but North America (USA, Canada, etc.) uses 011, Japan uses 010, Australia uses 0011, and many other countries use different prefixes.)