In the case of Kidderminster, there is only one block section, that to Bewdley South, and most of the bell signals which may be sent are shown in a box under the words 'SLBSBewdley'. When shown in black, they are appropriate at the time and may be sent by clocking on them. Those that are shown in grey are not appropriate at the time. Those that are shown in green indicate the bell signal that was last sent to you and clicking here will be understood as an acknowledgement of that bell signal.
A similar context-sensitive list of bells codes may be obtained from a MENU produced by clicking (with any button) over the brass plate on the block shelf for the relevant block section. Call attention is sent by clicking over the block instrument/bell.
The procedure that will be followed when a train is ready to approach is that a single beat on the bell is received ('call attention'), which should be acknowledged (by clicking over the block instrument/bell which stand on the block shelf just above the brass plate), after which a code is received which indicates the class of the train which is approaching. This may either be accepted, ignored or a train offered instead in the other direction.
To accept, it may be necessary to reverse an acceptance lever (at Kidderminster lever number 1 is the acceptance lever from Bewdley South and at Exeter West there are acceptance levers for wrong road movements down the up lines). To reverse the lever click on the button above the lever to release the electric lock and then click on the lever itself to reverse it. Repeat the same bell code in acknowledgement to accept the train.
When the approaching train passes the previous signalbox, the code 'train entering section' (2) is sent. This must be acknowledged. When the train has arrived clear of the section, the acceptance lever may be restored and the appropriate bell code (e.g. 'train out of section' (2-1)) sent. The train out of section bell signal will not be acknowledged.
When a departing train is offered (e.g. from Kidderminster to Bewdley), it will always be accepted in this simulation. This will release the section signal, 57, for a single pull. If this signal is put back to danger then it cannot be released again. In this case, or if a train is not to proceed, then the acceptance of the train may be cancelled by a special bell code. After sending 'call attention', the menu of bell codes obtained by clicking on the blue square or on the brass plate will contain an option 'cancelling' (3-5). Once acknowledged, a train may then be offered in either direction.
Working of Exeter West is complicated and some knowledge of the Absolute Block Signalling Regulations would be helpful. Alternatively why not visit the Heritage Centre at Crewe (the 'Railway Age') where the Exeter West signalbox has been recreated and full signalling simulations are enacted alternate weekends so you can see the object of the simulation being operated as it would have been twenty or thirty years ago.