Verb conjugation means changing a verb, so it is in the correct form in a sentence.
The bare infinitive form of the verb to walk is walk.
To put walk in the correct form for a sentence talking about the past we need to change it by adding -ed to the end:
Gary walked to the shop yesterday.
To put walk in the correct form for a sentence talking about a long action in the present we need to change it by adding is and -ing to the bare infinitive:
- is walking
Gary is walking to the shop now.