Wolunteering at an orphanage.
I have worked at an orphanage.
There were a lot of work to do.
I talked with children there and helped them with math. I taught them English, too. I was happy because I could help others.
(Would you check the passage above?)
I have volunteered at an orphanage. There was a lot of work to do. I talked with children there and helped them with math. I taught them English, too. I was happy because I could help others.
The passage you have written seems fine. However, there are a few minor grammatical corrections that I would suggest:
"Volunteering at an orphanage, I have worked at" instead of "Wolunteering at an orphanage. I have worked at."
"There was a lot of work to do" instead of "There were a lot of work to do."
"I talked with the children there and helped them with math. I also taught them English. I was happy because I could help others."
Overall, the passage effectively conveys your experience working at an orphanage and the tasks you undertook.