Hello friends I have one question about the channel width on my Mikrotik router, if I put it on 10mhz or 5mhz, could any computer connect to the Ap or I need a special wireless card that support it on the clients?

Thanks

You need

1.- Mikrotik radio that suports 5/10MHz (not all of them do)
2.- Client with radio with same capabilities

On Linux with Äthers card yes
On Windows I never seen 5 or 10 MHz Support

Thanks so if I need that some smarphones, tablet... conect to the Mikrotik Ap in addition to Mikrotik client I must to use minimum 20Mhz because the smarphone... can´t connect if I use a lower channel bandwith is it correct?

Exactly. If you're setting up an AP for unknown wireless/mobile devices you'll have to set it up in the most widely compatible way.

For 2.4GHz that means 20MHz and default settings.

Exactly. If you're setting up an AP for unknown wireless/mobile devices you'll have to set it up in the most widely compatible way.

For 2.4GHz that means 20MHz and default settings.

I have one doubt, I have two mikrotik router one as Ap and other as Ap client of the first both support 10mhz , is there any possibility that the two Mikrotik can work in 10mhz but the Mikrotik Ap can also work in 20mhz for example to get that other device like smarphone... can connect also to the ap?

I only need a stable link between the mikrotik but i need that other device can use the Ap

No. You can add virtual access points for diffferent SSID, VLAN, authentication method etc, but they must all have the same radio parameters (frequency, bandwidth etc).