Alrighty, here we go. A little tutorial in bearing only launch (BOL) attacks.
This will be from the SSM side of the coin, as this was easiest to whip up without building a test scenario, but the principle is the same, and I can provide one that depicts an ASM attack in due course if necessary.
Borrowing this time from your favorite scenario

, 'Middleweights', for Westpac.
At game start I am in control of BLUE ship group AOS, a trio of Japanese Maritime Self Defense Force (JMSDF) Hayabusa class missile armed patrol craft. Here's a pic:

They are patrolling northward in the East China Sea, just southwest of Nagasaki.
A friendly aircraft to the east soon gets a sniff of a surface ship contact to the north.

Now, ordinarily, we would probably try and confirm the identity of this contact before taking any offensive action.
But, to speed up things, I used the 'reveal all' keystroke to identify the contact as a closely knit group of four South Korean Sea Dolphin class gunboats. Here's a pic:

I soon have a solid fix (via the aircraft's ESM) on some but not all of the enemy gunboats.
I could engage normally here but instead choose to attack via a bearing only launch (BOL) with the Hayabusa's active radar guided Type 88/90 (SSM-1) surface to surface anti-ship missiles.
The range to target is roughly 75 nm, while maximum range of the SSM-1 is 81 nm. We're good to go.
I choose the BOL attack method by pressing 'b' on the keyboard.
A yellow circle appears on the Group Map showing the maximum engagement range of my available BOL weapons, as well as a pop up window prompting me to select a bearing for attack.

(Note as well the Unit Map showing the uncertain position of at least some units of the enemy group).
I select the attack bearing by pointing with my mouse and clicking on an appropriate part of the Group Map in cross hair fashion. The selected point will also serve as the activation point for my missile's terminal active radar seeker.

It is important here to take into account the speed of your target, its current (or likely) heading, as well as the speed of your missiles.
Subsonic missiles like the SSM-1 will have the minimum seeker acquisition range of 5 nm while faster, supersonic missiles (such as many of the Soviet/Russian weapons) will be able to exploit a full 20 nm. Also, a reminder that the seeker acquisition angle is limited to 45 degrees, so any target falling outside that cone will likely escape attack.
If the target is distant, traveling at high speed, and your missiles are subsonic, you run the risk of the target reaching - and passing - your missiles' activation point before the missiles actually get there. If that happens, the seeker will probably see nothing but empty ocean when it finally enables.
On the other hand, if you set your activation point too early, you run the chance of your missile locking onto and attacking some other contact, possibly even a friendly or neutral if the sea is crowded. (Accidentally sinking a friendly warship or a fishing boat tends to have detrimental effects on one's career path).
Once I have chosen a bearing and activation point by clicking on the map, I will get the weapons allocation pop up window.

I know I have four potential targets, and plenty of missiles, but to conserve firepower, I assign a total of three SSM-1 missiles, one from each Hayabusa. Since the missiles have no way of selecting individual targets, especially when they are grouped closely, I do not want to shoot a bunch of missiles and have them all homing on a single ship.
Moments after launch, I can see that my BLUE missile group AUM is enroute and that they have 37 nm (and 3 minutes 45 seconds) to go before reaching their activation point.

Now, that RED air group to the west caused me all kinds of grief during this missile engagement. Turns out it was a flight of F-15K Slam Eagles and they happily splashed my anti-ship missiles. I had to shoot again to repeat the engagement.
The next screenshot shows my missiles just 1 nm (and 3 seconds) from reaching their activation point.
Fortunately they are still in front of the enemy group and I have a good chance that when the missiles activate, they will pick up the targets and attack.

After seeker activation, the missiles continue on their previous course, searching for targets. As earlier stated, their seeker range is just 5 nm, and so promptly at 5 nm (and 30 seconds) from the enemy group, I get confirmation of lock on.
Note the phrase in the Unit Map display becomes 'Distance to 1st Target' rather than 'Distance to 1st Activation'.

During the resulting terminal engagement, two of my three missiles home on, strike and destroy the South Korean gunboat
Kilurki 267, while the third missile locked onto another target. That attack, unfortunately, resulted in a clean miss.

Hopefully this helps give you (and others following the thread) some idea of how the BOL attack mechanism in HCE works.