These are the paradoxes under which Oceania operates. "War is Peace" seems like it couldn't possibly be true, but Oceania is at war with its own people...the government suppresses them into submission and obedience. As long as they follow the rules, there is peace, even though there is the constant premise of war with one of the other countries.
"Freedom is slavery" seems untrue as well, however, upon closer inspection, that is exactly what is happening in Oceania. The Proles, who are the most free, are also the most impoverished...enslaved by their lack of money but free to do all other things including wearing makeup, singing, etc. The Party members have more "freedom," but they are enslaved by overbearing rules and also the fear of the consequences should they break the rules. Room 101 is the most enslaving factor.
"Ignorance is strength" is also true, although it seems a serious contradiction. Winston constantly mentions that the strength is with the Proles. They are the largest population in Oceania, and they are the most ignorant. There are no telescreens or rules in the Proles' community. They are the dumb masses...not realizing that they are the sole people who are capable of rebelling and winning true freedom for everyone. However, they are blissfully happy in their ignorance, so there is no reason for them to rise up. They are poor, but they have just enough to survive and find some semblance of happiness.