nmis8.3.9g some doubts

If you are logged, where can I logout, and finish de session?

The default authentication configuration for 8.3.9g is apache, this means that apache handles the logging in and out process.  As far as I know there is no code available to log you out using this authentication mode, the best way to logout would be to close your browser or use an in-cognito window (I understand that this is not a great answer).  

In newer versions of NMIS the "htpasswd" authentication mode has returned and it is the new default, it provides a logout button, I can help you get a newer version, just reply to this and I will help you out.

It´s possible to change interface graph description, by deffault in top of the grapbh we can see : <node> <interface> <graph-period> , and I wold like to see interface description.

This is possible, the graph titles are defined for each graph in the file that delcares how to create the graph, they can be found in nmis8/models/Graph-*.nmis.  The default graphs that are displayed when viewing an interface are autil, abits, pkts_hc, cbqos_in and cbqos_out.  The graph I am guessing you are looking for is Graph-abits.nmis.  Scrolling to the bottom of the file you will find: 

### nmis8/models/Graph-abits.nmis [line 32]
'title' => { 
 'short' => '$node: $ifDescr - $length', 
 'standard' => '$node: $ifDescr - $length from $datestamp_start to $datestamp_end' 
},
'vlabel' => { 
 'standard' => 'Packets/Second' 
}

The problem we run into now is that the description field isn't available for using, but thanks to open source and the GPL it's easy to add.  The code below adds:

$description = $IF->{$intf}{Description};

### nmis8/cgi-bin/rrdraw.pl [line 220]:
if ($intf ne "") {
 $indx = $intf;
 $description = $IF->{$intf}{Description}; # <- add this line
 $ifDescr = $IF->{$intf}{ifDescr};
 $ifSpeed = $IF->{$intf}{ifSpeed};
 if ($ifSpeed eq "auto" ) {
 $ifSpeed = 10000000;
 }
 $speed = convertIfSpeed($ifSpeed);
}

Now change the graph to display $description.   

### nmis8/models/Graph-abits.nmis [line 32]
'title' => { 
 'short' => '$description', 

NOTE: NMIS will not make the graph bigger to fit a long description, if the description is long you may not see the whole description.

And the last it´s, why can I see graph of port-channels for 4500, but not for 3750

NMIS models define a section called "nocollect".  If any of the rows in this section match the interface then it will not be displayed.  This helps NMIS display only interfaces that are important to you and keeps you from having to store a lot of info you don't need.

You can find out which model was used for your device by clicking on the device and looking at the description, in the case below the CiscoRouter model was used, this file can be found at nmis8/models/Model-CiscoRouter.nmis:

EG.

Let's say I connect NMIS to a Cisco device and NMIS uses the model nmis8/models/Model-CatalystIOS.nmis , inside this model I find this section: 

'nocollect' => {
 'Description' => '^#',
 'ifDescr' => 'sublayer|null|controller',
 'ifOperStatus' => 'null',
 'ifType' => 'other|softwareloopback|propVirtual|slip',
 'noDescription' => 'true'
 },

If any of these match an interface for my device that interface will not be displayed.  An explantion of these rules:

'Description' => '^#', The description starts with a #
'ifDescr' => 'sublayer|null|controller', the ifDescr contains sublayer, null or controller
'ifOperStatus' => 'null', the ifOperStatus is null
'ifType' => 'other|softwareloopback|propVirtual|slip', the ifType is other, software, oopback, propVirtual or slip
'noDescription' => 'true' the description is blank

So if you would like to display ifType's of software, simply remove software from the nocollect->ifType section of the model used for that device.

In your case I suspect that the description for your interface might be blank, but if this is not the case send me the information about your interface and I can help you try and solve why it does not appear.