Do you mean using emoticons and sitting just on your avatar? You can go straight there by clicking your avatar in the header- it will take you to the dress-up screen. This will allow you to toggle sitting and standing, but the emoticons that users wear on their avatars are all items that must be purchased in the marketplace. They can not simply be toggled on and off- the same is true with text that appears around avatars, it all belongs to one item or another.
Are you referring to virtual worlds? It's different for each one, you'd need to specify which one you are using. Here;
here are the options using towns, and
here are the options using zOMG.
I've pointed out the stance toggle, emoticons, and circled the text entry on both.