thee: Celia, as the ruling duke's daughter, uses the familiar term of address to Rosalind, who replies with the more formal 'you'.

learn: meaning to teach

righteously tempered: properly composed, tempered of the right ingredients, proportioned so virtuously; (to temper: to mix)

perforce: by force, forcibly

Rose: pronounced "Rose" as in the flower, not "Roz" as in "Rosalind"

to make sport withall: Rosalind suggests falling in love in order to devise sports (a diversion, entertainment). Celia advises only to love a man in sport (in jest) but not in earnest (genuinely, sincerely, of an intense passion or desire). If Rosalind is too earnest she may offer an earnest (promise of sexual intercourse). If Rosalind's man is a "good man" (vigorous fornicator) she will come off (orgasm) in (during) earnest (copulation) but she will not be able to come off (retreat) in honor (virginity intact). 

with safety of a pure blush: unmarked by shame, blushing only because of virgin modesty, without more damage than an innocent blush, mere, free of guilt

good houswife For-tune: The goddess Fortune was traditionally represented as blindfolded, controlling a wheel which turned from happiness to despair. She was often described and pictured as controlled human destiny by the turn of her wheel. In general the wheel signified the inconstancy and unpredictability of Fortune. However, in this instance Celia identifies Fortune's wheel with a spinning wheel. She uses the term houswife which frequently meant 'hussy', 'wanton' so Celia puns on this. 

honest: chaste, virtuous

reignes in gifts of the world: commands material possessions

lineaments of Nature: natural qualities such as virtue, wit, beauty