Jiyugaoka station is located on the Oimachi-line and the Toyoko-line . If you are visiting Tokyo for the first time then it will probably be easier for you to take the Toyoko-line from Shibuya station.
Once at Jiyugaoka, all you have to do is start wandering around. I got another full write up of a previous visit to Jiyugaoka
in this post.