I get about 2 bar from public WIFI at my house. I can connect and can"t use the internet. If i use the public wifi near the area i can access it. So i plan to buy wifi extender but i don"t know if it will help in my situation with 2 bar. I wonder if it will increase the signal many bar and can reach how far. Any suggestion ? The way to EXTEND your range is with a passive device.
You can either make a high gain antenna or buy one. It needs to be in a place whkere there are few or no obstacles. This s pseudo lino-of-sight thing.
Active devices, poser devices,  are a poor solution. They do not add power to the other end.
Here is a Google:
High Gain for Wi FI
Ignore the  OMNI  6 DB antenna on Google
 You need 12 db or better for best results.
(Let me know if the link does not work.)
I'd also LIKE to point out here that using public WiFi for anything other than very basic surfing is an extremely bad idea - Unless the access point requires you to enter a WPA passphrase when connecting (Not talking about the login page that may appear in your BROWSER), the wireless traffic will not be encrypted meaning that any information you submit to non-https sites (like this one) is sent completely unencrypted and available to attackers.  For example, if you log into this website I could fairly easily sniff the username and password you used.Yes, i am working at spare part com and i ask the shop in thefront that sell it and they say that it"s not very helpful too in this situation, it only can be used for 2-5 floor low wifi signal to make the extender work better. Actually it"s not free wifi , but they give me free hotspot when i subscribe the internet from them , and i can use that when i am in their network coverage.