The primary command he gave was:
A new commandment I give to you, that you love one another: just as I have loved you, you also are to love one another. 35 By this all people will know that you are my disciples, if you have love for one another.” (John 13:34–35, ESV)
He illustrated this command when he washed the disciples' feet (John 13:1-17). See What does washing of the feet symbolize in John 13:10? Matt. 5:43-48 shows the extent of loving one another to love one's enemies. Jesus commands to make disciples.
Go therefore and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, 20 teaching them to observe all that I have commanded you. And behold, I am with you always, to the end of the age.” (Matt. 28:19–20, ESV)
See What is the best translation of the participles in the Great Commission, Matt. 28:19-20?
The Greatest Commandment is:
But when the Pharisees heard that he had silenced the Sadducees, they gathered together. 35 And one of them, a lawyer, asked him a question to test him. 36 “Teacher, which is the great commandment in the Law?” 37 And he said to him, “You shall love the Lord your God with all your heart and with all your soul and with all your mind. 38 This is the great and first commandment. 39 And a second is like it: You shall love your neighbor as yourself. 40 On these two commandments depend all the Law and the Prophets.” (Matt. 22:34–40)
Jesus illustrated this with the parable of the Good Samaritan (Luke 10:25-37). See Given the dynamics of the words πλησίον and רֵעַ, what did Jesus illustrate with the Good Samaritan?
I don't recall Jesus giving it as an actual commandment, but it is implied:
Then they said to him, “What must we do, to be doing the works of God?” 29 Jesus answered them, “This is the work of God, that you believe in him whom he has sent.” (John 6:28–29, ESV)
Probably he does in John 14:1:
Ye believe … believe also (πιστευετεελλιψκαι πιστευετε...και πιστευετε [pisteuete...kai pisteuete]). So translated as present active indicative plural second person and present active imperative of πιστευω [pisteuō]. The form is the same. Both may be indicative (ye believe … and ye believe), both may be imperative (believe … and believe or believe also), the first may be indicative (ye believe) and the second imperative (believe also), the first may be imperative (keep on believing) and the second indicative (and ye do believe, this less likely). Probably both are imperatives (Mark 11:22), “keep on believing in God and in me.” -- Robertson, A. T. (1933). Word Pictures in the New Testament (Jn 14:1). Broadman Press.