Like Griff said, you're missing commas seperating field definitions. It also helps to indent your code properly and capitalize SQL keywords to make it easier to read:
CREATE TABLE Buysfrom (
Cid int,
Bid int,
Hrs int,
CONSTRAINT buys_PK PRIMARY KEY (Cid, Bid),
CONSTRAINT customer_Buys_PK FOREIGN KEY (Cid) REFERENCES customer (Customer_id),
CONSTRAINT Branch_Buys_FK FOREIGN KEY (Bid) REFERENCES Branch (Branch_id)
);