Here is a schedule.
I need to take Donan bus from Station Toyako to Lake View Nonokaze Hotel at Toyako Onsen in the afternoon. Next morning, I need take back to Toyako Station. I can't understand the chart. Can somebody help me with that?
The table is indeed puzzling. From the annotation 行先 (destination) on the top left corner, it seems to me that the buses don't all go to the same destination. For example, the 6:25 bus from the Tōyako-onsen station will eventually go to Mareppu, while the 7:00 bus will take you to Muroran Port.
That being said, as you are travelling only between Tōya-ekimae (洞爺駅前) and Tōyako-onsen (洞爺湖温泉), you may safely ignore the top row. Then, read it as you would any bus schedule.
For example, the 18:45 bus from Tōya-ekimae will stop at Yakubamae (役場前) at 18:48, will not stop at Sakaemachi (栄町), and will stop at Nishiyama Yūhodō (西山遊歩道) at 18:58, etc. It will arrive at Tōyako-onsen at 19:03. Then, you can read all other timetables the same way.
(I assume that you do read some Japanese, as the website doesn't have English at all)