How can i make an item, talk?

Go to Basic Tools and enter a dialogue. Find the dialogue in the Workspace and put it in the object you want to "talk". From there you can edit the dialogue and what type of dialogue it is.

Dialogue (user interacts): Go into your Advanced objects under the insert tab (Using ribbon) and insert a Dialogue in the specific part; or, go into basic objects and insert a dialogue (classic studio layout). It is the same object, just different paths.

Or to have a part "talk" on a set cycle without user interaction:

create a model and then insert the part you want to have talking and name it "Head". Insert a humanoid and inside the head insert a script. Here is what you want it to look like:

while true do

script.Parent.Parent.Name = "Text" --you can change the text to whatever you want the message to be. After this is optional unless you want it to display more than one message.
wait(1) --As always, you can change the value to however long you like.
script.Parent.Parent.Name = "Text" --again change the text to your message.
wait(1) --and you can just repeat it over and over again until all of your messages are displayed.
end

Alternately you could put the script in the model itself, but you would have to change the script.Parent.Parent.Name to match

script.Parent.Name = ""

to get the name of the model itself changed and not the workspace or the model that the model is in (if it is in a larger model).

Try this video, it helped me a lot on this subject:

https://www.youtube.com/watch?v=pb4uDPReAF0