The verb iku (行く) means go. Iku is a slightly irregular verb. The conjugation for the te/ta form is itte & itta. In all other forms it follows the regular conjugation rules.
(I) wont go with jon = jon to ikanai (ジョンさんと行かない)
Jon will go = jonsan wa iku (ジョンさんは行く)
Since iku is a motion verb it's often seen with the particle ni.
(I am) going to school = gakkou ni iku (学校に行く)
(I) went to park = kouen ni itta (公園に行った)
(My) child wont go to school = kodomo wa gakkou ni ikanai
(I am) going to work = shigoto ni ikimasu (仕事に行きます)
The verb kuru (来る) means to come. It is a irregular verb. You must memorize the different forms of this verb. Here is a list of the conjugations using the forms we have already learned.
Come to (my) house please = uchi ni kite kudasai (家に来てください)
Today, (you) didn't come to school = kyou gakkou ni konakatta