If a clan’s initial offer or demand isn’t quite what you had in mind you can use the counter-offer option to enable further negotiation to take place, rather than simply rejecting it.
The threaten option is a diplomatic tool to help you get your own way in certain situations. The effectiveness of a threat greatly depends on the military strength of the clan you are threatening relative to your own, so you must not use the option without fully considering what it means to do so - making threats you cannot or choose not to back up will result in them becoming less effective each time you use them. It must also be borne in mind when making threats that the threatened party will not look kindly upon those who like to throw their military weight around - your diplomatic relations will suffer drastically, eventually leading to war between you. If you are threatened by another clan, refusal to comply with their wishes may mean they instantly declare war on you, so you must be sure of your military strength before doing so.