Assim has two main meanings: like this & like that
Eu sou assim. I'm like that.
Eu sempre fui assim. I've always been like this.
Comendo assim vou me engordar. Eating like this I'll get fat.
Assim can also mean, as soon as.
When used like this it triggers the future subjunctive tense.
future subjunctive Assim que voce chegar. As soon as you arrive.
future subjunctive Assim que eu terminar. As soon as I finish.