I am new to apex and wondering if someone help me to do... 

update picklist from lookup value..

Example:- If i select india in lookup the picklist has to get updated as india.

whatever the value is selected in lookup needs to get updated in picklist.
I have 248 values needs to be updated.

I need to update my picklist value Nationality__C from the lookup value nationalitylookup__c .

If the lookup value is "kuwait" i have to update the picklist as "Kuwait". Whatever the value is in lookup it has to gt updated in picklist value.
 

I need to update my picklist value Nationality__C from the lookup value nationalitylookup__c .

If the lookup value is "kuwait" i have to update the picklist as "Kuwait". Whatever the value is in lookup it has to gt updated in picklist value.
 

how to update a lookup field in an custom object based on the picklist field on opportunity both are related??

I have a list of values in one picklist field (A) and would like to have some of those values (abc, dfe) trigger to update another picklist field's (B) value (xyz) upon selection. The reason i would like to use Apex is because I have a field dependency already used for those fields and cannot overwrite it with another dependency. Any suggestion? I am new to apex and I have trouble creating the trigger.