Learn Polish: Ten dom jest stary i mały. - This house is old and small.

In Polish, i is used to connect two similar things that simply go together, like two adjectives describing the same house. The word a is used when you want to show a slight contrast or a change of subject, like saying "This house is old, and/while that one is new" (Ten dom jest stary, a tamten jest nowy).

Could we use ale (but) in this sentence instead of i?

Yes, you could say Ten dom jest stary, ale mały (This house is old, but small). However, you usually use ale when the second part is unexpected. Since being old and being small often go together naturally, i is the most standard choice here to just link the facts.

Why is it ten dom instead of to dom?

Because dom (house) is a masculine noun, we must use the masculine word for "this", which is ten. You would use to if you were just pointing and saying "This is a house" (To jest dom), but when "this" directly attaches to a specific noun (like "this house"), it has to match that noun's gender.

Why do both stary and mały end with -y?

Adjectives in Polish change their endings to match the gender of the noun they describe. Since dom is a masculine noun (you can usually tell because it ends in a consonant, like m), both "old" and "small" take the standard masculine singular ending -y.