Lay and lie are both irregular verbs. If you memorize their forms, then you’ll avoid making common errors.

Simple present:

• The chicken lays eggs.
• I lie on the sofa.

Simple past:

• The chicken laid eggs yesterday.
• I lay on the sofa yesterday.

Present Continuous:

• The chicken is laying eggs right now.
• I am lying on the sofa right now.

Present Perfect:

• The chicken has laid eggs.
• I have lain on the sofa.