I wish to send data fromo a greenhouse to the Cloud and see that there is a gateway close to me in UK/Hursley Road - how do I go about connecting to it and what range of devices are available ?
Buy a device, set it up with the documentation both the device vendor & the TTN provide, et voila!
You don’t connect to a gateway as such, it just hears radio signals and if they fit the right format, passes the information on to the central servers - you don’t need permission as such.
As to what range of devices are available, you can build one for around £5 or pay £100’s, there are literally hundreds on the market, perhaps Mr Google can help.
[If you mean’t range in distance, then typically up to 10-15km with line of sight is the norm]
Thanks. What does the device need to conform to ? I’m new to all of this.
Ideally look for a LoRaWAN Certified (LoRa Alliance - https://lora-alliance.org/) or compliant device - unless looking to build your own - in which case follow the available guidelines (GIYF) and ensure you have a LoRaWAN rules following device so as not to disrupt other users or devices (see TTN Documentation - https://www.thethingsnetwork.org/docs/ ). Make sure you follow both the legal (power/duty cycle, etc. as approriate) rules and the TTN fair use policy. If new to LoRa/LoRaWAN best start with lots of background reading and trawlining through all the valuable (ok, if somewhat fragnmented!) info here on the forum. Perhaps look to the LoRaWAN academy lessons ( https://lora-developers.semtech.com/resources/lorawan-academy/ ) to understand more and if looking for ready made devices you can do worse than start here https://www.thethingsnetwork.org/marketplace/products/devices
Hursley Road…where? Eastleigh/Southampton, Havant/Portsmouth, other town? (Check local UK Map for local community - https://www.thethingsnetwork.org/country/united-kingdom/ Southampton = https://www.thethingsnetwork.org/community/southampton/ ) If former then reach out to Steve over at the Uni of So’ton or friend of the community Rich at Semtech (IIRC runs several GW’s in the area) or any of the other active local community members or the guys at Portsmoouth (newer/smaller community).
If you exhaust background checks and reading and you have a well framed question with specific needs/issues e.g. on a device, a development or use case, that you can articulate with supporting info/data then post to the forum and there will always be people willing to try and assist… just be wary of asking questions without having checked for info and searched forum or wider internet 1st as that can be perceived as lazy behaviour! 
Thanks Jeff - comments noted and will read all the link !! Hursley Road= in Chandlers Ford, I see a gateway close by, hence the original question.