Step 1: Understanding the words "altar" and "alter".
- Altar: A raised structure, often used for religious or ceremonial purposes.
- Alter: To change or modify something.
Step 2: Usage in sentences.
- They prayed at the altar in the church.
- He decided to alter his plans after considering the risks. Final Answer:
\[
\boxed{\text{They prayed at the altar in the church. He decided to alter his plans after considering the risks.}}
\]