Not sure how you got CrystalDiskMark to produce those results. 3 are standard CDM results, 1 is not, and you're missing 1 which is standard.
Sequential is the speed at reading/writing big files. So if you were copying a bunch of 1GB movie files (which weren't fragmented), the sequential speed is what you'd expect. For a modern 7200 RPM drive, it ranges from about 80-160 MB/s today.
4k is the speed at reading/writing really small files (4KB in size). On many larger drives, this is the smallest cluster size, so it's the lower speed limit. There's OS and drive overhead in locating the file, then the time associated with moving the read/write head to the proper location and waiting for the right section of the platter to spin under the head. For a modern drive, it's about 0.7-1.3 MB/s.
QD32 is queue depth of 32. That is, you queue up a bunch of read/writes in the drive, and the drive does them as quickly as it can. It doesn't make much difference on HDDs since you're mostly limited by the physical speed of the platter and read/write head. On SSDs it can make a huge difference reading small files, since the time it takes for the drive to transfer the data to the computer can be a lot longer than the time to read the data. For SSDs, 4k read/write speeds of about 25-70 MB/s is typical. With a QD32, this can reach 200-400 MB/s. The drive is reading/writing multiple files in parallel from the perspective of the computer.
The benchmark you're missing is the 512k scores. This tests speed of 512 KB files, which as you can guess is between the 4k and sequential speeds. This varies a lot from drive to drive (especially for SSDs where I've seen it range from 25 - 300 MB/s). It's typical of the speed you'd expect if you were copying a folder full of MP3s or office documents.
External USB 2.0 drives maxed out at about 25-30 MB/s. USB 3.0 drives can theoretically hit over 300 MB/s, but I've seen poor implementations which have trouble exceeding 50 MB/s. It would appear your external drive is one of these. Unless your 1 TB drive is almost full?