Golang中=和<-有什么区别

func worker(id int, jobs <-chan int, results chan<- int) {
    for j := range jobs {
        fmt.Println("worker", id, "processing job", j)
        time.Sleep(time.Second)
        results <- j * 2
    }
}

func main() {
    t := time.Now()
    fmt.Println(t)
    jobs := make(chan int, 100)
    results := make(chan int, 100)
    for w := 1; w <= 4; w++ {
        go worker(w, jobs, results)
    }
    for j := 1; j <= 20; j++ {
        jobs <- j
    }
    close(jobs)
    for a := 1; a <= 20; a++ {
        <-results
    }

    t = time.Now()
    fmt.Println(t)
}

我对“ <-”感到困惑，找不到关于“ <-”的任何相关文档。那么<-和= ??有什么区别？为什么我不能在这里使用=？