Myr Welder has only the activated abilities of cards it exiles. It doesn't gain triggered abilities or static abilities.

Activated abilities contain a colon. They're generally written "[Cost]: [Effect]." Some keywords are activated abilities; they have colons in their reminder text.

If an activated ability of a card exiled with Myr Welder references the card it's printed on by name, treat Myr Welder's version of that ability as though it referenced Myr Welder by name instead. For example, if Lux Cannon (which says, in part, "{T}: Put a charge counter on Lux Cannon.") has been exiled by Myr Welder, Myr Welder has the ability "{T}: Put a charge counter on Myr Welder."