Nested IF and IFS Formula Builder

Help me create a formula with multiple conditions:

**Logic Requirements:**
Describe your conditions in plain language:
- If [condition 1], then [result 1]
- Else if [condition 2], then [result 2]
- Else if [condition 3], then [result 3]
- Otherwise, [default result]

**Example with Specifics:**
| Condition | Result |
|-----------|--------|
| [e.g., Score >= 90] | [e.g., "A"] |
| [e.g., Score >= 80] | [e.g., "B"] |
| [e.g., Score >= 70] | [e.g., "C"] |
| [Default] | [e.g., "F"] |

**Data Location:**
- Cell to evaluate: [e.g., A2]
- Result should go in: [e.g., B2]

**Additional Complexity:**
- Multiple criteria per condition (AND/OR): [Yes/No - explain]
- Check across multiple columns: [Yes/No]
- Handle errors/blanks: [Yes/No]

**Excel Version:**
- [ ] Microsoft 365 / 2019+ (has IFS function)
- [ ] Excel 2016 or earlier (nested IF only)
- [ ] Google Sheets

Please provide:
1. Nested IF formula
2. IFS formula alternative (if applicable)
3. SWITCH formula alternative (if applicable)
4. Explanation of formula logic
5. Tips for maintaining readability
6. When to consider VLOOKUP/XLOOKUP instead