Hi,
Yes you will need a UIManager in order for the tk2d buttons to work: In the hierarchy window select 'Create > tk2d > UI Manager'. Once it's created, select it in the hierarchy window then drag your scene camera onto the 'UI Camera' slot in the Inspector window.
tk2d provides a number of different button and UI prefabs which can be found in 'Project > TK2DROOT > tk2dUI_demo > ControlPrefabs'. Drag the BasicButton prefab into your hierarchy window and select it. If you expand the button object, the ButtonGraphic will let you select one of the existing sprites from the default UIDemoSpriteCollection, or you can use a sprite from another collection. You may need to scale the size of the button sprite up depending on your camera settings. If you do change the scale of the button graphic, remember to click on 'Fit' in 'Tk 2d UIItem > Collider > Automatic Fit' to ensure the collider is the same size as your button.
Finally, you can drag a game object that contains a script onto 'Send Message > Target', which will then allow you to select which functions are called depending on the state of the button e.g. 'On Click', On Up' etc. e.g. If you have an arrow pointing right as your button graphic, you might link this to a function 'MoveRight' when the button is clicked.
I hope this clarifies things for you.
Thanks.