っぽい is typically used with adjectives and nouns to give your verdict on something based on how something looks or acts. Used with i-adjectives the final い of the adjective is dropped.
| A cheap-looking bag. | 
Context: Regardless of the price, you think the bag looks cheap.
It can simply be added to nouns.
| Childish. | 
っぽい almost always carries a negative connotation and so the following is unnatural:
| おいしっぽい | 
| [Delicious-looking food.] | 
Here we would use 〜そう instead.
| おいしそうな | 
| Delicious-looking food. | 
You may also see it used with the verb “to be angry” and “to forget”. Here we need the verb stem.
| Short-tempered. | 
| Forgetful. | 
While not “proper” Japanese, young people may attach it to the end of the standard form of the verb as a sort of colloquialism.
| Something seems to be bothering her. |