Here are the answers to the Pandas questions:
1. A pandas Series is a one-dimensional labeled array capable of holding any data type (integers, strings, floating point numbers, Python objects, etc.). The axis labels are collectively called index.
2. A DataFrame is a two-dimensional size-mutable, potentially heterogeneous tabular data structure with labeled axes (rows and columns). It is a DataFrame that contains columns, which may be of different value types (numeric, string, boolean etc.).
3. To create an empty DataFrame:
```python
import pandas as pd
df = pd.DataFrame()
```
4. To fill missing values in a DataFrame, we can use fillna()