ANOVA planned contrasts

Dear TalkStats community,

Previously a website ( was recommended to me on ANOVA and planned contrasts. The page is very useful, however there are some parts of the description which are hard to follow for me. Could you help me please to clarify these parts?

1) The equation above can be used to calculate both between subject and within subject contrasts?
2) Could you tell me please what 'n' means in the equation? Is this the number of participants in the study, the second degree of freedom in the F-test or something else?
3) If I got the value of Fcontrast how can I calculate the p value from that? Am I understand correctly, that the Fcontrast value is an F value?
4) Are the degree of freedoms of this F value 1; n-k respectively (where n is the number of participants and k is the number of groups in the within- or between-subject factor)?

Thank you very much for your kind help in advance!