Buy at Ask, Sell at Bid
When trading remember that there are always 2 quotes present: Bid and Ask.
The difference between Bid and Ask rate determines the width of the spread.
What rates you will always open and close your positions with, Bid or Ask?
this depends on whether you Sell or Buy:
Buy position is opened at the Ask rate.
Sell position is opened at the Bid rate.
Buy position is closed at the Bid rate.
Sell position is closed at the Ask rate.