start by resetting your 2-7210s http://www.tp-link.com/en/article/?faqid=202
assign different IPs to both of them they have to be out of your DHCP scope, this IPs have to be in the subnet of your router, this is default IP of 7210 radio 192.168.0.254 example, if your router is 192.168.1.0 #1 7210 set it to 192.168.1.11 and #2-7210 192.168.1.12 that change is made in Network/Lan
bridge mode tuto here http://www.tp-link.com/en/article/?faqid=176 notice on step #6 you will have to use WEP security no other, for that reason is not recommended, your Throughput will be half.
this setting works better, and its a standard on PTPs, set #1 AP mode there are not dedicated tutos for your model but AP mode its the easiest read this one as guide http://www.tp-link.com/en/article/?faqid=378 if you dont get it come back and ask i will write a AP mode setting for you, and set #2 as Client here http://www.tp-link.com/en/article/?faqid=318 the thing here is that Client mode will only deliver internet by lan cable you will have to add a router or convert one to AP to have wireless internet.
you need LOS (line of sight), i know its a short distance but no obstructions.
or you can set 7210 #2 as AP Client Router, this will deliver wire and wireless internet here http://www.tp-link.com/en/article/?faqid=289 this setting will be useless if #2 7210 is on the roof.

I set up the two products TL-WA7210N with the same SSID as my wireless network at point

at this moment use a dif SSID from your wireless network, you will know if your PTP its working, once you get it set desire SSID

Hello
Thanks for your explanation
I did the same as your answer except bridge with WPA and not WEP.
I will really get crazy with these devices.
Can you help me ( you will find the diagram of my network enclosed )
first of all my request:
I want only a bridge connexion without local wireless on a 7210
By witch 7210 I begin the setup ? Building A or B ?
Can you help step by step for setting these two devices in my Network ?
Thanks

Im going to asume building A that has the Archer where is the internet provider (ISP)
1-as told before reset your 2-7210s to factory default
2-Quick Set up,next window Operation Mod ,select third row Acces Point, click to next window
Wireless Network Name(SSID) for the moment write france, region yours i asume is France
and agree with terms and accept. if you do not do this change and leave United States, your
7210 will be more powerfull, but dont ask me about legal regulations in France, for the moment
I would use United States. from your post I asume you are in France.
power and security default, Wireless Password. what ever you want, click next, like i told you before,
same subnet as your ISP router, if you dont know it write 192.168.3.254
subnet mask in America we use 255.255.255.0 no more changes in this window, click next, and will be
ask to reboot, once rebooted, the POE the little white box, on Lan side connect your ethernet cable from Archer
and in a minute, you have wireless internet, thats part #1.
To set 7210 that will be on building B, the first 7210 has to be powered on and close where you are doing settings
could be the same room but not too close, at least 3 meters a part.or more if possible
you start the same once reset it to defaults, Quick set up Operation Mode in this case will
be Client, its last row, next window you will click survey takes some seconds to pop a new window,
and you will find and choose the SSID france that you have named #1 to the right click CONNECT
you go back to seme window, check first 2 rows are filled with france and Mac
same country and security you had set on #1 IP be carefull here last digit has to be different
192.168.3.25 3 and Subnet mask 255.255.255.0 next click reboot, let reboot andthat is all,
now you connect to POE your computer by Lan cable, and you have internet or connection to
building A
a cable and you have wire internet.

Hello Danymarc
You are right I am in France:)
If i undertsand well, I will not use bridge mode but in building A acces point and building B client.
Can I use WPA or WEP ?

I will try this evening, I hope all will be find
thanks again

No bridge mode
No WPA or WEP
Use WPA/WPA2 PERSONAL it's defaults

thanks again
I will try
see you

hello again
If I want in building B wireless conexion, how I can setup the 7210
thanks

With 7210 as Client no way
Operation Mode as Client Router yes. but in your scenario
useless cause your drawing is on the roof
connect any TL router by lan cable from 7210 to a 740 router converted to AP
you do not use wan port blue one in this setting use any of the 4 yellow lan ports
guide here http://www.tp-link.com/en/article/?faqid=417
you are getting ahead, get your PTP first
you are going to have issues, it's not as transparent as you read it.
As security leave default see picture do not mess with WEP or WPA/WPA2 - Enterprise

Ok thanks again
I will try this week end

Hello Danymarc
Thanks again
Everything works perfectly
But why these devices doesn't work in Bridge mode ?