Vlan Tagging at Access Port in Switch

switchport trunk encapsulation dot1q does not apply to access mode ports.

Vlan Tags are only pushed on the packet if it comes in untagged and egresses a trunk port; otherwise, the packet's vlan is simply tracked internally in the switch. Packets ingress to an access vlan port are tagged with that same vlan on the trunk port. The only exception is a packet that is on the trunk port's native vlan (default, vlan 1 on Cisco switches)

This answer on stackoverflow should clarify

The statement

switchport trunk encapsulation dot1q

is needed (on some) cisco switches to explicitly set the trunking mode as there are switches where ISL trunking is also available. On other (mostly smaller desktop) switches it produces an error (because dot1q is the only trunking mode there).

When you set the port to trunk mode with

switchport mode trunk

statements like

switchport trunk .... 

comes to play

When the port is in access mode with:

switchport mode access

statements like

switchport access ...

comes to play.

One can easily check port settings with:

show running-config interface f0/1

EDIT: Beware as other vendors use different terminology.

On HP trunking = port aggregation.
On Cisco etherchannel = port aggregation.